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Germline mutations in the BRCA1 and BRCA2 genes are characterized by deficient repair of DNA double-strand breaks by homologous recombination. Defective DNA double-strand break repair has been not only implicated as a key contributor to tumorigenesis in mutation carriers but also represents a potential target for therapy. The transcriptional similarities between BRCA1-deficient tumors and sporadic tumors of the basal-like subtype have led to the investigation of homologous recombination repair-directed therapy in triple-negative tumors, which demonstrates overlap with the basal-like subtype. We broaden the scope of this topic by addressing a "repair-defective" rather than "BRCA1-like" phenotype. We discuss structural and functional aspects of key repair proteins including BRCA1, BRCA2, BRCA1 interacting protein C-terminal helicase 1, and partner and localizer of BRCA2 and describe the phenotypic consequences of their loss at the cellular, tissue, and organism level. We review potential mechanisms of repair pathway dysfunction in sporadic tumors and address how the identification of such defects may guide the application of repair-directed therapies. [ABSTRACT FROM AUTHOR]

Alpelisib is a selective inhibitor of PI3Kα, shown to improve outcomes for PIK3CA mutant, hormone receptor positive (HR+) metastatic breast cancers (MBC) when combined with antiestrogen therapy. To uncover mechanisms of resistance, we conducted a detailed, longitudinal analysis of tumor and plasma circulating tumor DNA among such patients from a phase I/II trial combining alpelisib with an aromatase inhibitor (AI) (NCT01870505). The trial's primary objective was to establish safety with maculopapular rash emerging as the most common grade 3 adverse event (33%). Among 44 evaluable patients, the observed clinical benefit rate was 52%. Correlating genetic alterations with outcome, we identified loss-of-function PTEN mutations in 25% of patients with resistance. ESR1 activating mutations also expanded in number and allele fraction during treatment and were associated with resistance. These data indicate that genomic alterations that mediate resistance to alpelisib or antiestrogen may promote disease progression and highlight PTEN loss as a recurrent mechanism of resistance to PI3Kα inhibition., Competing Interests: Competing Interests P.R. reports consulting or advisory role for Novartis, AstraZeneca, Foundation Medicine, and institutional research support from Illumina and GRAIL; M.N.D. is an employee of Eli Lilly, P.D.S. reports consulting with Tmnity and research funding from AstraZeneca; B.T.L. reports consulting/advisory board for Genentech, ThermoFisher Scientific, Guardant Health, Hengrui Therapeutics, Mersana Therapeutics, Biosceptre Australia and institutional research support from Illumina, GRAIL, Genentech, AstraZeneca; N.V. reports consulting or advisory role for Novartis; K.J. reports consulting or advisory role for ADC Therapeutics; AstraZeneca; Jounce therapeutics; Novartis; Pfizer; Spectrum; Taiho, research funding from ADC Therapeutics (Inst); Clovis Oncology (Inst); Debio (Inst); Genentech (Inst); Novartis (Inst); Novita (Inst); Pfizer (Inst) and other relationship with Jounce Therapeutics; Novartis; Pfizer; Taiho; A.C. reports being an advisory board member for Accurate Medical a Stockholder for Amgen; L.N. reports honoraria from Advanced Breast Cancer 4 International Consensus Conference; Bluprint Oncology Concepts; Celgene; Context Therapeutics; MCI Breast Cancer Symposium, consulting or advisory role for Advanced Breast Cancer International Consensus Conference; Bluprint Oncology Concepts; Celgene; Context Therapeutics; MCI Breast Cancer Symposium and travel, accommodations, expenses from Advanced Breast Cancer International Consensus Conference; Celgene; MCI Breast Cancer Symposium; A.S., R.J.N., J.I.O., and R.B.L. are employees and stockholders of Guardant Health; M.E.R. reports honoraria from AstraZeneca, consulting or advisory role for AstraZeneca; McKesson; Merck; Pfizer, research funding from Abbvie (Inst); AstraZeneca (Inst); InVitae (Inst); Medivation (Inst); Myriad Genetics (Inst); Tesaro (Inst), and travel, accommodations, expenses from AstraZeneca; M.E.L. reports serving as a consultant or speaking for Legacy Healthcare Services, Adgero Bio, Amryt, Celldex, Debiopharm, Galderma, Johnson & Johnson, Novocure, Lindi, Merck, Sharp and Dohme Corp, Helsinn Healthcare SA, Janssen Research & Development LLC, Menlo Therapeutics, Novartis, Roche, AbbVie, Boehringer Ingelheim, Allergan, Amgen, E. R. Squibb & Sons, LLC, EMD Serono, AstraZeneca, Genentech, Leo Pharma, Seattle Genetics, Bayer, Manner, SAS, Lutris, Pierre Fabre, Paxman Coolers, Adjucare, Dignitana, Biotechspert, Teva Mexico, Parexel, OnQuality, Novartis, Our Brain Bank, and Takeda Millenium; and receiving research funding from Veloce, US Biotest, Berg, BMS, Lutris, Paxman, and Novocure; J.S.R-F reports personal/consultancy fees from VolitionRx, Page.AI, Goldman Sachs, Grail, Ventana Medical Systems, Roche, Genentech and Invicro; D.B.S. received honoraria and consulted for Pfizer, Loxo, Vivideon, Illumina and Lilly Oncology; M.S. is in the Advisory Board of Bioscience Institute and Menarini Ricerche, received research funds from Puma Biotechnology, Daiichi Sankyo, Targimmune, Immunomedics and Menarini Ricerche, is a co-founder of Medendi Medical Travel and received honoraria from Menarini Ricerche and ADC; S.C. reports institutional research funding from Novartis, Eli Lilly, Sanofi, Daiichi Sankyo, Genentech and Ad hoc consulting for Novartis, Context Therapeutics, Sermonix, Eli Lilly, BMS, and Revolution Medicine. The other coauthors report no competing interests.

Purpose Phosphatidylinositol-4, 5-bisphosphate 3-kinase catalytic subunit alpha ( PIK3CA) mutations are frequently observed in primary breast cancer. We evaluated their prognostic relevance by performing a pooled analysis of individual patient data. Patients and Methods Associations between PIK3CA status and clinicopathologic characteristics were tested by applying Cox regression models adjusted for age, tumor size, nodes, grade, estrogen receptor (ER) status, human epidermal growth factor receptor 2 (HER2) status, treatment, and study. Invasive disease-free survival (IDFS) was the primary end point; distant disease-free survival (DDFS) and overall survival (OS) were also assessed, overall and by breast cancer subtypes. Results Data from 10,319 patients from 19 studies were included (median OS follow-up, 6.9 years); 1,787 patients (17%) received chemotherapy, 4,036 (39%) received endocrine monotherapy, 3,583 (35%) received both, and 913 (9%) received none or their treatment was unknown. PIK3CA mutations occurred in 32% of patients, with significant associations with ER positivity, increasing age, lower grade, and smaller size (all P < .001). Prevalence of PIK3CA mutations was 18%, 22%, and 37% in the ER-negative/HER2-negative, HER2-positive, and ER-positive/HER2-negative subtypes, respectively. In univariable analysis, PIK3CA mutations were associated with better IDFS (HR, 0.77; 95% CI, 0.71 to 0.84; P < .001), with evidence for a stronger effect in the first years of follow-up (0 to 5 years: HR, 0.73; 95% CI, 0.66 to 0.81; P < .001; 5 to 10 years: HR, 0.82; 95% CI, 0.68 to 0.99; P = .037); > 10 years: (HR, 1.15; 95% CI, 0.84 to 1.58; P = .38; P heterogeneity = .02). In multivariable analysis, PIK3CA genotype remained significant for improved IDFS ( P = .043), but not for the DDFS and OS end points. Conclusion In this large pooled analysis, PIK3CA mutations were significantly associated with a better IDFS, DDFS, and OS, but had a lesser prognostic effect after adjustment for other prognostic factors.

BRCA1 is essential for homology-directed repair (HDR) of DNA double-strand breaks in part through antagonism of the nonhomologous end-joining factor 53BP1. The ATM kinase is involved in various aspects of DNA damage signaling and repair, but how ATM participates in HDR and genetically interacts with BRCA1 in this process is unclear. To investigate this question, we used the Brca1 S1598F mouse model carrying a mutation in the BRCA1 C-terminal domain of BRCA1. Whereas ATM loss leads to a mild HDR defect in adult somatic cells, we find that ATM inhibition leads to severely reduced HDR in Brca1 S1598F cells. Consistent with a critical role for ATM in HDR in this background, loss of ATM leads to synthetic lethality of Brca1 S1598F mice. Whereas both ATM and BRCA1 promote end resection, which can be regulated by 53BP1, 53bp1 deletion does not rescue the HDR defects of Atm mutant cells, in contrast to Brca1 mutant cells. These results demonstrate that ATM has a role in HDR independent of the BRCA1-53BP1 antagonism and that its HDR function can become critical in certain contexts., Competing Interests: The authors declare no conflict of interest.

Background: The current analysis was performed to evaluate the impact of PIK3CA hotspot mutations on everolimus efficacy in BOLERO-2 participants, using cell-free DNA (cfDNA) from plasma samples collected at the time of patient randomisation., Methods: PIK3CA H1047R, E545K, and E542K mutations in plasma-derived cfDNA were analysed by droplet digital PCR (ddPCR). Median PFS was estimated for patient subgroups defined by PIK3CA mutations in each treatment arm., Results: Among 550 patients included in cfDNA analysis, median PFS in everolimus vs placebo arms was similar in patients with tumours that had wild-type or mutant PIK3CA (hazard ratio (HR), 0.43 and 0.37, respectively). Everolimus also prolonged median PFS in patients with PIK3CA H1047R (HR, 0.37) and E545K/E542K mutations (HR=0.30) with a similar magnitude., Conclusions: Mutation analysis of plasma-derived cfDNA by ddPCR suggests that PFS benefit of everolimus was maintained irrespective of PIK3CA genotypes, consistent with the previous analysis of archival tumour DNA by next-generation sequencing.

The mammary gland undergoes significant proliferative stages after birth, but little is known about how the developmental changes impact DNA double-strand break (DSB) repair. Mutations in multiple genes involved in homology-directed repair (HDR), considered a particularly accurate pathway for repairing DSBs, are linked to breast cancer susceptibility, including BRCA2. Using reporter mice that express an inducible endonuclease, we find that HDR is particularly robust in mammary tissue during puberty and pregnancy, accounting for 34-40% of detected repair events, more than in other tissues examined. Brca2 hypomorphic mutation leads to HDR defects in mammary epithelium during puberty and pregnancy, including in different epithelial lineages. Notably, a similar dependence on Brca2 is observed in other proliferative tissues, including small intestine epithelium. Our results suggest that the greater reliance on HDR in the proliferating mammary gland, rather than a specific dependence on BRCA2, may increase its susceptibility to tumorigenesis incurred by BRCA2 mutation.

Importance: Estrogen receptor α (ESR1) mutations found in metastatic breast cancer (MBC) promote ligand-independent receptor activation and resistance to estrogen-deprivation therapy in laboratory models. The prevalence of these mutations and their potential impact on clinical outcomes has not been established., Objective: To determine the prevalence of ESR1 mutations (Y537S and D538G) in estrogen receptor (ER)-positive MBC and determine whether mutation is associated with inferior outcomes., Design, Setting, and Participants: From December 16, 2014, to August 26, 2015, we analyzed cell-free DNA (cfDNA) from baseline plasma samples from participants in the BOLERO-2 double-blind phase 3 study that randomized patients from 189 centers in 24 countries with MBC to exemestane plus placebo or exemestane plus everolimus. The study enrolled postmenopausal women with a diagnosis of MBC and prior exposure to an aromatase inhibitor. Baseline plasma samples were available from 541 of 724 patients (74.7%). We assessed the effect of mutation on overall survival of the population and the effect of mutation on progression-free survival (PFS) by treatment arm., Interventions: Patients were randomized to treatment with exemestane (25 mg oral daily) together with everolimus (10 mg oral daily) or with placebo., Main Outcomes and Measures: The 2 most frequent mutations in ESR1 (Y537S and D538G) were analyzed from cfDNA using droplet digital polymerase chain reaction and samples scored as wild-type, D538G, Y537S, or double mutant. Cox-proportional hazards model was used to assess PFS in patient subgroups defined by mutations, and the effect of each mutation on overall survival., Results: Of 541 evaluable patients, 156 (28.8%) had ESR1 mutation D538G (21.1%) and/or Y537S (13.3%), and 30 had both. These mutations were associated with shorter overall survival (wild-type, 32.1 months [95% CI, 28.09-36.40 months]; D538G, 25.99 months [95% CI, 19.19-32.36 months]; Y537S, 19.98 months [13.01-29.31 months]; both mutations, 15.15 months [95% CI, 10.87-27.43 months]). The D538G group (hazard ratio, 0.34 [95% CI, 0.02-0.57]) derived a similar PFS benefit as wild type from addition of everolimus to exemestane., Conclusions and Relevance: ESR1 mutations are prevalent in ER-positive aromatase inhibitor-treated MBC. Both Y537S and D538G mutations are associated with more aggressive disease biology., Trial Registration: clinicaltrials.gov Identifier: NCT00863655., Competing Interests: Disclosures: Drs Chen, He, Patel, and Voi are employees of Novartis. Dr Chandarlapaty has received consulting fees from AstraZeneca. No other disclosures are reported.

Purpose: To investigate whether anti-vascular endothelial growth factor therapy with bevacizumab prolongs progression-free survival (PFS) when added to first-line letrozole as treatment of hormone receptor-positive metastatic breast cancer (MBC)., Patients and Methods: Women with hormone receptor-positive MBC were randomly assigned 1:1 in a multicenter, open-label, phase III trial of letrozole (2.5 mg orally per day) with or without bevacizumab (15 mg/kg intravenously once every 3 weeks) within strata defined by measurable disease and disease-free interval. This trial had 90% power to detect a 50% improvement in median PFS from 6 to 9 months. Using a one-sided α = .025, a target sample size of 352 patients was planned., Results: From May 2008 to November 2011, 350 women were recruited; 343 received treatment and were observed for efficacy and safety. Median age was 58 years (range, 25 to 87 years). Sixty-two percent had measurable disease, and 45% had de novo MBC. At a median follow-up of 39 months, the addition of bevacizumab resulted in a significant reduction in the hazard of progression (hazard ratio, 0.75; 95% CI, 0.59 to 0.96; P = .016) and a prolongation in median PFS from 15.6 months with letrozole to 20.2 months with letrozole plus bevacizumab. There was no significant difference in overall survival (hazard ratio, 0.87; 95% CI, 0.65 to 1.18; P = .188), with median overall survival of 43.9 months with letrozole versus 47.2 months with letrozole plus bevacizumab. The largest increases in incidence of grade 3 to 4 treatment-related toxicities with the addition of bevacizumab were hypertension (24% v 2%) and proteinuria (11% v 0%)., Conclusion: The addition of bevacizumab to letrozole improved PFS in hormone receptor-positive MBC, but this benefit was associated with a markedly increased risk of grade 3 to 4 toxicities. Research on predictive markers will be required to clarify the role of bevacizumab in this setting., Competing Interests: Authors’ disclosures of potential conflicts of interest are found in the article online at www.jco.org. contributions are found at the end of this article., (© 2016 by American Society of Clinical Oncology.)

Poly(ADP-ribose) polymerases (PARPs) are the first proteins involved in cellular DNA repair pathways to be targeted by specific inhibitors for clinical benefit. Tumors harboring genetic defects in homologous recombination (HR), a DNA double-strand break (DSB) repair pathway, are hypersensitive to PARP inhibitors (PARPi). Early phase clinical trials with PARPi have been promising in patients with advanced BRCA1 or BRCA2-associated breast, ovary and prostate cancer and have led to limited approval for treatment of BRCA-deficient ovary cancer. Unlike HR-defective cells, HR-proficient cells manifest very low cytotoxicity when exposed to PARPi, although they mount a DNA damage response. However, the genotoxic effects on normal human cells when agents including PARPi disturb proficient cellular repair processes have not been substantially investigated. We quantified cytogenetic alterations of human cells, including primary lymphoid cells and non-tumorigenic and tumorigenic epithelial cell lines, exposed to PARPi at clinically relevant doses by both sister chromatid exchange (SCE) assays and chromosome spreading. As expected, both olaparib and veliparib effectively inhibited poly-ADP-ribosylation (PAR), and caused marked hypersensitivity in HR-deficient cells. Significant dose-dependent increases in SCEs were observed in normal and non-tumorigenic cells with minimal residual PAR activity. Clinically relevant doses of the FDA-approved olaparib led to a marked increase of SCEs (5-10-fold) and chromatid aberrations (2-6-fold). Furthermore, olaparib potentiated SCE induction by cisplatin in normal human cells. Our data have important implications for therapies with regard to sustained genotoxicity to normal cells. Genomic instability arising from PARPi warrants consideration, especially if these agents will be used in people with early stage cancers, in prevention strategies or for non-oncologic indications.

Genetic abnormalities are present in all tumor types, although the frequency and type can vary. Chromosome abnormalities include highly aberrant structures, particularly chromothriptic chromosomes. The generation of massive sequencing data has illuminated the scope of the mutational burden in cancer genomes, identifying patterns of mutations (mutation signatures), which have the potential to shed light on the relatedness and etiologies of cancers and impact therapy response. Some mutation patterns are clearly attributable to disruptions in pathways that maintain genomic integrity. Here we review recent advances in our understanding of genetic changes occurring in cancers and the roles of genome maintenance pathways., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Purpose: To evaluate the feasibility of delivering experimental radiation therapy to tumors in the mouse pancreas. Imaging and treatment were performed using combined CT (computed tomography)/orthovoltage treatment with a rotating gantry., Methods and Materials: After intraperitoneal administration of radiopaque iodinated contrast, abdominal organ delineation was performed by x-ray CT. With this technique we delineated the pancreas and both orthotopic xenografts and genetically engineered disease. Computed tomographic imaging was validated by comparison with magnetic resonance imaging. Therapeutic radiation was delivered via a 1-cm diameter field. Selective x-ray radiation therapy of the noninvasively defined orthotopic mass was confirmed using γH2AX staining. Mice could tolerate a dose of 15 Gy when the field was centered on the pancreas tail, and treatment was delivered as a continuous 360° arc. This strategy was then used for radiation therapy planning for selective delivery of therapeutic x-ray radiation therapy to orthotopic tumors., Results: Tumor growth delay after 15 Gy was monitored, using CT and ultrasound to determine the tumor volume at various times after treatment. Our strategy enables the use of clinical radiation oncology approaches to treat experimental tumors in the pancreas of small animals for the first time. We demonstrate that delivery of 15 Gy from a rotating gantry minimizes background healthy tissue damage and significantly retards tumor growth., Conclusions: This advance permits evaluation of radiation planning and dosing parameters. Accurate noninvasive longitudinal imaging and monitoring of tumor progression and therapeutic response in preclinical models is now possible and can be expected to more effectively evaluate pancreatic cancer disease and therapeutic response., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Purpose: The CLEOPATRA (Clinical Evaluation of Trastuzumab and Pertuzumab) study demonstrated superior progression-free survival (PFS) and overall survival when pertuzumab was added to trastuzumab and docetaxel. Paclitaxel given once per week is effective and less toxic than docetaxel. We performed a phase II study to evaluate the efficacy and safety of pertuzumab and trastuzumab with paclitaxel given once per week., Patients and Methods: Patients with metastatic human epidermal growth factor receptor 2-positive breast cancer with zero to one prior therapy were enrolled. Treatment consisted of paclitaxel 80 mg/m(2) once per week plus trastuzumab (8 mg/kg loading dose → 6 mg/kg) once every 3 weeks plus pertuzumab (840 mg loading dose → 420 mg) once every 3 weeks, all given intravenously. The primary end point was 6-month PFS assessed by Kaplan-Meier methods., Results: From January 2011 to December 2013, we enrolled 69 patients: 51 (74%) and 18 (26%) treated in first- and second-line metastatic settings, respectively. At a median follow-up of 21 months (range, 3 to 38 months), 6-month PFS was 86% (95% CI, 75% to 92%). The median PFS was 19.5 months (95% CI, 14 to 26 months) overall. PFS was 24.2 months (95% CI, 14 months to not reached [NR]) and 16.4 months (95% CI, 8.5 months to NR) for those without and with prior treatment, respectively. At 1 year, Kaplan-Meier PFS was 70% (95% CI, 56% to 79%) overall, 71% (95% CI, 55% to 82%) for those without prior therapy, and 66% (95% CI, 40% to 83%) for those with prior therapy. Treatment was well-tolerated; there was no febrile neutropenia or symptomatic left ventricular systolic dysfunction., Conclusion: Paclitaxel given once per week with trastuzumab and pertuzumab is highly active and well tolerated and seems to be an effective alternative to docetaxel-based combination therapy., (© 2014 by American Society of Clinical Oncology.)

Background: Ganetespib is a small molecule, nongeldanamycin HSP90 inhibitor with potent inhibitory effects on HSP90-dependent oncoproteins of relevance to breast cancer pathogenesis. We therefore tested ganetespib in an unselected cohort of patients with MBC., Patients and Methods: Patients were treated with single agent ganetespib at 200 mg/m(2) once weekly for 3 weeks, on a 28-day cycle. Therapy was continued until disease progression. The primary end point was ORR using Reponse Evaluation Criteria in Solid Tumors version 1.1., Results: Twenty-two patients were enrolled with a median age of 51(range, 38-70) years and a median Eastern Cooperative Oncology Group performance status of 0 (range, 0-1). Most patients had at least 2 previous lines of chemotherapy in the metastatic setting. Most common toxicities, largely grade 1/2, were diarrhea, fatigue, nausea, and hypersensitivity reaction. The ORR in this unselected population was 9%, with all responses coming from the subset of patients with HER2-positive MBC (2/13; 15%). One patient with TNBC had objective tumor regression in the lung metastases. The clinical benefit rate (complete response + partial response + stable disease > 6 months) was 9%, median progression-free survival was 7 weeks (95% confidence interval [CI], 7-19), and median overall survival was 46 weeks (95% CI, 27-not applicable)., Conclusion: The study did not meet the prespecified criteria for ORR in the first stage of the Simon 2-stage model in this heavily pretreated unselected population of MBC. However, activity was observed in trastuzumab-refractory HER2-positive and TNBC. Ganetespib was well tolerated and responses in more targeted populations harboring specific HSP90-dependent oncoproteins justifies its further study, particularly as part of rational combinations., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Purpose: Patients with hormone receptor-negative breast cancer generally do not benefit from endocrine-targeted therapies. However, a subset with androgen receptor (AR) expression is predicted to respond to antiandrogen therapies. This phase II study explored bicalutamide in AR-positive, estrogen receptor (ER), and progesterone receptor (PgR)-negative metastatic breast cancer., Experimental Design: Tumors from patients with ER/PgR-negative advanced breast cancer were tested centrally for AR [immunohistochemistry (IHC) > 10% nuclear staining considered positive]. If either the primary or a metastatic site was positive, patients were eligible to receive the AR antagonist bicalutamide at a dose of 150 mg daily. Clinical benefit rate (CBR), the primary endpoint, was defined as the total number of patients who show a complete response (CR), partial response (PR), or stable disease (SD) > 6 months; secondary endpoints included progression-free survival (PFS) and toxicity. Correlative studies included measurement of circulating endocrine markers and IHC surrogates for basal-like breast cancer., Results: Of 424 patients with ER/PgR-negative breast cancer, 12% tested AR-positive. The 6-month CBR was 19% [95% confidence interval (CI), 7%-39%] for bicalutamide. The median PFS was 12 weeks (95% CI, 11-22 weeks). Bicalutamide was well-tolerated with no grade 4/5 treatment-related adverse events observed., Conclusion: AR was expressed in 12% of patients with ER/PgR-negative breast cancer screened for this trial. The CBR of 19% observed with bicalutamide shows proof of principle for the efficacy of minimally toxic androgen blockade in a select group of patients with ER/PgR-negative, AR-positive breast cancer., (©2013 AACR.)

Background: Nanoparticle albumin-bound paclitaxel (nab-P) and bevacizumab have each demonstrated efficacy in patients with MBC. This trial was designed to further develop nab-P by evaluating its efficacy and safety using every 3 weeks (q3w), every 2 weeks (q2w), or weekly scheduling in combination with bevacizumab as first-line treatment of MBC., Patients and Methods: This open-label phase II study randomized patients to nab-P 260 mg/m(2) q3w (arm A) vs. 260 mg/m(2) q2w with filgrastim (arm B) vs. 130 mg/m(2) weekly uninterrupted, all with bevacizumab (15 mg/kg q3w arm A, 10 mg/kg q2w arms B and C). The primary endpoints were overall response rate (ORR) and toxicity. Time to tumor progression (TTP) and overall survival were secondary endpoints., Results: Of 212 patients randomized, 208 (arm A, 75; arm B, 54; arm C, 79) were treated. Arm B was closed early due to toxicity, with more grade ≥ 2 fatigue (arm A, 46%; arm B, 62%; arm C, 62%) and bone pain (arm A, 11%; arm B, 23%; arm C, 5%). Neurotoxicity grade ≥ 2 was equivalent across the arms (> 50%) and reversible for most patients. Febrile neutropenia occurred in ≤ 3% of patients in all arms. ORR was similar among the arms (arm A, 45%; arm B, 41%; arm C, 46%). Median TTP was slightly longer in arm C (9.0 months) vs. arms A (8.0 months) and B (5.8 months) (overall, P = .105)., Conclusions: Significant antitumor activity was observed in all the arms. Weekly nab-P with bevacizumab appeared to have the highest therapeutic index. However, sensory neuropathy was treatment limiting, which suggests that a 3 weeks on and 1 week off schedule should be explored., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Homology-directed repair (HDR) is a critical pathway for the repair of DNA double-strand breaks (DSBs) in mammalian cells. Efficient HDR is thought to be crucial for maintenance of genomic integrity during organismal development and tumor suppression. However, most mammalian HDR studies have focused on transformed and immortalized cell lines. We report here the generation of a Direct Repeat (DR)-GFP reporter-based mouse model to study HDR in primary cell types derived from diverse lineages. Embryonic and adult fibroblasts from these mice as well as cells derived from mammary epithelium, ovary, and neonatal brain were observed to undergo HDR at I-SceI endonuclease-induced DSBs at similar frequencies. When the DR-GFP reporter was crossed into mice carrying a hypomorphic mutation in the breast cancer susceptibility gene Brca1, a significant reduction in HDR was detected, showing that BRCA1 is critical for HDR in somatic cell types. Consistent with an HDR defect, Brca1 mutant mice are highly sensitive to the cross-linking agent mitomycin C. By contrast, loss of the DSB signaling ataxia telangiectasia-mutated (ATM) kinase did not significantly alter HDR levels, indicating that ATM is dispensable for HDR. Notably, chemical inhibition of ATM interfered with HDR. The DR-GFP mouse provides a powerful tool for dissecting the genetic requirements of HDR in a diverse array of somatic cell types in a normal, nontransformed cellular milieu.

Testicular Germ Cell Tumors (TGCT) and patient-derived cell lines are extremely sensitive to cisplatin and other interstrand cross-link (ICL) inducing agents. Nevertheless, a subset of TGCTs are either innately resistant or acquire resistance to cisplatin during treatment. Understanding the mechanisms underlying TGCT sensitivity/resistance to cisplatin as well as the identification of novel strategies to target cisplatin-resistant TGCTs have major clinical implications. Herein, we have examined the proficiency of five embryonal carcinoma (EC) cell lines to repair cisplatin-induced ICLs. Using γH2AX staining as a marker of double strand break formation, we found that EC cell lines were either incapable of or had a reduced ability to repair ICL-induced damage. The defect correlated with reduced Homologous Recombination (HR) repair, as demonstrated by the reduction of RAD51 foci formation and by direct evaluation of HR efficiency using a GFP-reporter substrate. HR-defective tumors cells are known to be sensitive to the treatment with poly(ADP-ribose) polymerase (PARP) inhibitor. In line with this observation, we found that EC cell lines were also sensitive to PARP inhibitor monotherapy. The magnitude of sensitivity correlated with HR-repair reduced proficiency and with the expression levels and activity of PARP1 protein. In addition, we found that PARP inhibition strongly enhanced the response of the most resistant EC cells to cisplatin, by reducing their ability to overcome the damage. These results point to a reduced proficiency of HR repair as a source of sensitivity of ECs to ICL-inducing agents and PARP inhibitor monotherapy, and suggest that pharmacological inhibition of PARP can be exploited to target the stem cell component of the TGCTs (namely ECs) and to enhance the sensitivity of cisplatin-resistant TGCTs to standard treatments.

PIK3CA gene mutations are the most common activating mutations in human breast cancer. Its association with hormone receptor-positive breast cancer makes it a prime target for clinical therapeutic advances to maintain anti-estrogen responsiveness. In anticipation of this therapeutic approach, we have evaluated intratumoral heterogeneity in primary breast cancers with regard to PIK3CA mutation status. In addition, we have assessed for the presence of the mutation in paired pre-invasive breast cancer and metastases. To assess for intratumoral heterogeneity, separate tumor blocks from primary breast cancers (n = 63) were genotyped for PIK3CA mutations. Available paired tissue samples from breast tumors known to harbor mutations underwent massARRAY genotyping (n = 70) to identify PIK3CA and AKT1(E17K) mutations. Cores were macro-dissected from matched tissue, including normal breast, benign lymph nodes (LN), ductal carcinoma in situ, regional LN metastases, and distant metastases. Matched samples underwent genetic fingerprinting by multiple SNP genotyping to confirm genetic identity. Intratumoral heterogeneity is minimal with a concordance rate of 95.2% between two different blocks from primary breast cancers. Complete concordance of PIK3CA mutations is noted between primary breast cancer and DCIS. PIK3CA mutations in primary breast cancer are detected in matched regional LNs (91.7%) and distant metastases (100%). Mutation detection by massARRAY genotyping is sensitive but may be affected by sample quality. Intratumoral heterogeneity as measured by PIK3CA genotype is rare; PIK3CA mutations occur early and are selected for in breast cancer progression. HapMap analysis is an essential control for paired sample analysis. This data is clinically important, particularly, for the design of therapies targeting the PI3K/AKT pathway, as it offers confidence that the detection of PIK3CA mutations in the invasive primary tumor will accurately reflect breast cancer biology.

Purpose: HSP90 is a chaperone protein required for the stability of a variety of client proteins. 17-Demethoxygeldanamycin (17-AAG) is a natural product that binds to HSP90 and inhibits its activity, thereby inducing the degradation of these clients. In preclinical studies, HER2 is one of the most sensitive known client proteins of 17-AAG. On the basis of these data and activity in a phase I study, we conducted a phase II study of 17-AAG (tanespimycin) with trastuzumab in advanced trastuzumab-refractory HER2-positive breast cancer., Experimental Design: We enrolled patients with metastatic HER2(+) breast cancer whose disease had previously progressed on trastuzumab. All patients received weekly treatment with tanespimycin at 450 mg/m(2) intravenously and trastuzumab at a conventional dose. Therapy was continued until disease progression. The primary endpoint was response rate by Response Evaluation Criteria in Solid Tumors (RECIST) criteria., Results: Thirty-one patients were enrolled with a median age of 53 years and a median Karnofsky performance status (KPS) of 90%. The most common toxicities, largely grade 1, were diarrhea, fatigue, nausea, and headache. The overall response rate was 22%, the clinical benefit rate [complete response + partial response + stable disease] was 59%, the median progression-free survival was 6 months (95% CI: 4-9), and the median overall survival was 17 months (95% CI: 16-28)., Conclusions: This is the first phase II study to definitively show RECIST-defined responses for 17-AAG in solid tumors. Tanespimycin plus trastuzumab has significant anticancer activity in patients with HER2-positive, metastatic breast cancer previously progressing on trastuzumab. Further research exploring this therapeutic interaction and the activity of HSP90 inhibitors is clearly warranted., (©2011 AACR.)

Purpose: Bevacizumab confers benefits in metastatic breast cancer but may be more effective as adjuvant therapy. We evaluated the cardiac safety of bevacizumab plus dose-dense doxorubicin-cyclophosphamide (ddAC) → nanoparticle albumin-bound (nab)-paclitaxel in human epidermal growth factor receptor 2 normal early-stage breast cancer., Experimental Design: Eighty patients with normal left ventricular ejection fraction (LVEF) were enrolled. Bevacizumab was administered for 1 year, concurrently with ddAC → nab-paclitaxel then as a single agent. LVEF was evaluated at months 0, 2, 6, 9, and 18. This regimen was considered safe if fewer than three cardiac events or fewer than two deaths from left ventricular dysfunction occurred. Correlative studies of cardiac troponin (cTn) and plasma renin activity (PRA) were conducted., Results: The median age was 48 years (range, 27-75 years), and baseline LVEF was 68% (53%-82%). After 39 months' median follow-up (5-45 months): median LVEF was 68% (53%-80%) at 2 months (n = 78), 64% (51%-77%) at 6 months (n = 66), 63% (48%-77%) at 9 months (n = 61), and 66% (42%-76%) at 18 months (n = 54). One patient developed symptomatic LV dysfunction at month 15. Common toxicities necessitating treatment discontinuation were hypertension (HTN, 4%), wound-healing complications (4%), and asymptomatic LVEF declines (4%). Neither cTn nor PRA predicted congestive heart failure (CHF) or HTN, respectively., Conclusions: Bevacizumab with ddAC → nab-paclitaxel had a low rate of cardiac events; cTn and PRA levels are not predictive of CHF or HTN, respectively. The efficacy of bevacizumab as adjuvant treatment will be established in several ongoing phase III trials., (©2011 AACR.)

Homologous recombination (also termed homology-directed repair, HDR) is a major pathway for the repair of DNA interstrand cross-links (ICLs) in mammalian cells. Cells from individuals with Fanconi anemia (FA) are characterized by extreme ICL sensitivity, but their reported defect in HDR is mild. Here we examined ICL-induced HDR using a GFP reporter and observed a profound defect in ICL-induced HDR in FA cells, but only when the reporter could replicate.

Cancer-specific alterations in DNA methylation are hallmarks of human malignancies; however, the nature of the breast cancer epigenome and its effects on metastatic behavior remain obscure. To address this issue, we used genome-wide analysis to characterize the methylomes of breast cancers with diverse metastatic behavior. Groups of breast tumors were characterized by the presence or absence of coordinate hypermethylation at a large number of genes, demonstrating a breast CpG island methylator phenotype (B-CIMP). The B-CIMP provided a distinct epigenomic profile and was a strong determinant of metastatic potential. Specifically, the presence of the B-CIMP in tumors was associated with low metastatic risk and survival, and the absence of the B-CIMP was associated with high metastatic risk and death. B-CIMP loci were highly enriched for genes that make up the metastasis transcriptome. Methylation at B-CIMP genes accounted for much of the transcriptomal diversity between breast cancers of varying prognosis, indicating a fundamental epigenomic contribution to metastasis. Comparison of the loci affected by the B-CIMP with those affected by the hypermethylator phenotype in glioma and colon cancer revealed that the CIMP signature was shared by multiple human malignancies. Our data provide a unifying epigenomic framework linking breast cancers with varying outcome and transcriptomic changes underlying metastasis. These findings significantly enhance our understanding of breast cancer oncogenesis and aid the development of new prognostic biomarkers for this common malignancy.

Mutations in BRCA1 predispose to tumorigenesis presumably from the inability to accurately repair DNA double-strand breaks by homologous recombination. Two new papers shed light on how loss of the DNA damage response protein 53BP1 reverses phenotypes of BRCA1 mutant cells, with potential clinical implications., ((c) 2010 Elsevier Inc. All rights reserved.)

Mitotic homologous recombination promotes genome stability through the precise repair of DNA double-strand breaks and other lesions that are encountered during normal cellular metabolism and from exogenous insults. As a result, homologous recombination repair is essential during proliferative stages in development and during somatic cell renewal in adults to protect against cell death and mutagenic outcomes from DNA damage. Mutations in mammalian genes encoding homologous recombination proteins, including BRCA1, BRCA2 and PALB2, are associated with developmental abnormalities and tumorigenesis. Recent advances have provided a clearer understanding of the connections between these proteins and of the key steps of homologous recombination and DNA strand exchange.

Purpose: In breast cancer, somatic mutations in the PIK3CA gene are common. The prognostic implication of these activating mutations remains uncertain as moderately sized studies have yielded variable outcomes. Our aim was to determine the prognostic implications of PIK3CA mutations in breast cancer., Experimental Design: Archival formalin-fixed paraffin-embedded primary breast tumors, from 590 patients selected for known vital status with a median follow-up of 12.8 years and a tumor >1 cm, were genotyped for PIK3CA mutations. Mutation rates and associations between mutation site and clinicopathologic characteristics were assessed. Progression-free survival, overall survival, and breast cancer-specific survival were examined using Kaplan-Meier or competing risk methodology., Results: PIK3CA mutation is identified in 32.5% of breast cancers. PIK3CA mutation significantly associates with older age at diagnosis, hormone receptor positivity, HER2 negativity, lower tumor grade and stage, and lymph node negativity. Patients with PIK3CA mutated tumors have significant improvement in overall survival (P = 0.03) and breast cancer-specific survival (P = 0.004). Analysis for PIK3CA mutation site-specific associations reveals that the H1047R kinase domain mutation highly associates with node negativity (P = 0.007), whereas helical domain hotspot mutations associate with older age at diagnosis (P = 0.004)., Conclusion: This study defines the positive prognostic significance of PIK3CA mutations. This work is clinically relevant, as it will significantly affect the design of clinical trials planned for phosphatidylinositol 3-kinase-targeted therapy. Future work may define a population of older age breast cancer patients in whom therapy can be minimized.

Purpose: We conducted a pilot study of dose-dense epirubicin/cyclophosphamide (EC) x 6 --> paclitaxel (P) x 6 with pegfilgrastim. A previous dose-dense trial of FEC (5-fluorouracil [5-FU]/EC) x 6 with filgrastim --> by weekly paclitaxel alternating with docetaxel x 18 was not feasible because of pneumonitis (with dose-dense FEC) and pericardial/pleural effusion (taxane phase). Dose-dense EC (without the 5-FU) is not associated with pneumonitis, and dose-dense paclitaxel (alone) is feasible. Primary objective was feasibility., Patients and Methods: Patients with resectable breast cancer were enrolled, regardless of surgery status, tumor size, or nodal status. Treatment regimen consisted of every-2-week EC (100/600 mg/m2) x 6 --> by 2-weekly P (175 mg/m2) x 6 with pegfilgrastim 6 mg on day 2., Results: Between November 2004 and May 2005, 38 patients were enrolled. The median age was 47 years (range, 30-72 years); 33 of 38 (87%) were treated in the adjuvant setting and 27 of 33 (81%) had involved nodes (range, 1-46); 5 of 38 (13%) were treated pre-operatively; 33 of 38 (87%) completed all chemotherapy as planned; the remaining patients (13%) had treatment modifications for toxicity. Febrile neutropenia occurred in 6 of 38 patients (16 %) and only during EC. There were 12 hospitalizations in 9 of 38 patients (24%) enrolled., Conclusion: Dose-dense every-2-week EC x 6 --> P x 6 with pegfilgrastim is feasible based on our prospective definition.

Background: Imatinib mesylate is a potent inhibitor of Abl, KIT, and PDGFR tyrosine kinases. Breast cancer has variable expression of KIT and PDGFR therefore we conducted a phase II trial to evaluate the safety and efficacy of imatinib in patients with metastatic breast cancer (MBC)., Patients and Methods: Eligible patients had measurable and progressive MBC, with no limits on prior chemo- or hormonal therapy. Imatinib was initially administered at a dose of 400 mg orally twice a day with provisions for dose reductions based on toxicities. The primary endpoint was clinical benefit based on RECIST criteria. Tumor specimens were tested for expression of KIT and PDGFR tyrosine kinases., Results: Sixteen patients were enrolled and treated. Median age was 55 years (range: 35-73); median number of prior chemotherapy regimens for MBC was 4 (range 1-8). The main non-hematologic toxicities were (Grades 1/2; Grade 3): fatigue (56%; 6%), edema (38%; 19%), nausea (31%; 19%), vomiting (38%; 0%), anorexia (38%; 0%), diarrhea (19%; 6%), and rash (25%; 6%). Grade 3/4 hematologic and biochemical abnormalities were minimal. There was no evidence of clinical benefit. The median duration of therapy on trial was 28 days (range 2-71). Of the 13 testable cases: 1 was KIT positive and 4 were PDGFR positive., Conclusion: Imatinib therapy at doses of 800 mg/day was associated with significant toxicity in patients with heavily pre-treated MBC. Our results do not indicate activity for imatinib monotherapy in these unselected patients.

Purpose: To develop a potentially superior adjuvant chemotherapy regimen, we conducted a pilot study of dose-dense 5-fluorouracil, epirubicin, and cyclophosphamide (FEC) followed by weekly alternating taxanes. The primary objective was to determine the feasibility of the regimen; the secondary objective was to estimate the disease-free and overall survival., Experimental Design: Patients with >/=4 node-positive breast cancer were studied. Treatment consisted of FEC at 500/100/500 mg/m(2), respectively, x6 at two-week intervals with granulocyte colony-stimulating factor, followed by weekly paclitaxel (80 mg/m(2)) alternating with docetaxel (35 mg/m(2)) x18., Results: Between November 2001 and January 2003, 44 patients were enrolled. Median age was 46 years (range, 26-63 years), median number of positive nodes was 9 (range, 4-32), and median tumor size was 2.5 cm (range, 0.6-11.0 cm). Because of unexpected toxicities, the study was stopped when 17 (39%) had fully completed all of the planned treatment. Two of 17 (12%) developed grade 4 pericardial/grade 3 bilateral pleural effusions at treatment completion; both required pericardial window. The remaining patients were treated with taxanes using one of several standard dose and schedule combinations. Furthermore, 4 of 44 (9%) developed pneumonitis attributed to the FEC regimen. Hospital admissions were required for 12 of 44 (27%); 3 of 44 (7%) required blood transfusions. There were no treatment related deaths. Median disease-free and overall survival will not be estimatable because of early closure of study., Conclusion: FEC x6 at 2-week intervals followed by 18 weeks of alternating taxanes is not feasible at the doses tested. Other strategies are needed to improve adjuvant systemic chemotherapy.

Mus81-Eme1 endonuclease has been implicated in the rescue of stalled replication forks and the resolution of meiotic recombination intermediates in yeast. We used gene targeting to study the physiological requirements of Mus81 in mammals. Mus81-/- mice are viable and fertile, which indicates that mammalian Mus81 is not essential for recombination processes associated with meiosis. Mus81-deficient mice and cells were hypersensitive to the DNA cross-linking agent mitomycin C but not to gamma-irradiation. Remarkably, both homozygous Mus81-/- and heterozygous Mus81+/- mice exhibited a similar susceptibility to spontaneous chromosomal damage and a profound and equivalent predisposition to lymphomas and other cancers. These studies demonstrate a critical role for the proper biallelic expression of the mammalian Mus81 in the maintenance of genomic integrity and tumor suppression.

Yeast and human Eme1 protein, in complex with Mus81, constitute an endonuclease that cleaves branched DNA structures, especially those arising during stalled DNA replication. We identified mouse Eme1, and show that it interacts with Mus81 to form a complex that preferentially cleaves 3'-flap structures and replication forks rather than Holliday junctions in vitro. We demonstrate that Eme1-/- embryonic stem (ES) cells are hypersensitive to the DNA cross-linking agents mitomycin C and cisplatin, but only mildly sensitive to ionizing radiation, UV radiation and hydroxyurea treatment. Mammalian Eme1 is not required for the resolution of DNA intermediates that arise during homologous recombination processes such as gene targeting, gene conversion and sister chromatid exchange (SCE). Unlike Blm-deficient ES cells, increased SCE was seen only following induced DNA damage in Eme1-deficient cells. Most importantly, Eme1 deficiency led to spontaneous genomic instability. These results reveal that mammalian Eme1 plays a key role in DNA repair and the maintenance of genome integrity.

The BRCA1 tumor suppressor has been implicated in the maintenance of chromosomal stability through homology-directed repair of DNA double-strand breaks. Much of the BRCA1 in cells forms a heterodimeric complex with a structurally related protein BARD1. We report that expression of truncated mouse or human BARD1 peptides capable of interacting with Brca1 results in a homologous-repair deficiency. Repair is mildly reduced in Brca1 wild-type cells and severely reduced in cells that harbor a Brca1 splice product deleted for exon 11. Nuclear localization of the Brca1 or BARD1 peptides is not compromised, implying that the repair deficiency is caused by a more direct effect on repair. The tumor suppressor activity of BRCA1 may require the participation of BARD1 to maintain chromosome integrity through the homologous-repair pathway.

BRCA1 and BRCA2 mutations are estimated to be responsible for the great majority of familial breast and ovarian cancers. Much progress has been made toward the understanding of the function of these proteins through genetic, biochemical, and structural studies. The embryonic lethality encountered in the knockout mouse initially hindered the development of mouse models aimed at studying tumor suppression. However, mice that harbor hypomorphic Brca1 and Brca2 alleles and cre-mediated tissue-specific deletions for Brca1 and Brca2 have been generated. Mice deficient for either Brca1 or Brca2 sustain a wide range of carcinoma and mammary epithelium deleted for Brca1 or Brca2 is highly susceptible to mammary tumorigenesis. Mammary (and other) tumors occur at long latency as compared to oncogene-induced mouse tumors. p53 deficiency is highly cooperative with both Brca1 and Brca2 in promoting tumorigenesis. Analysis of Brca1-associated mammary tumors reveals significant similarities to BRCA1-associated breast cancer in regard to high tumor grade, hormone receptor negativity, a high incidence of p53 mutations and genetic instability.

Disruption of the gene encoding RAD51, the protein that catalyzes strand exchange during homologous recombination, leads to the accumulation of chromosome breaks and lethality in vertebrate cells. As RAD51 is implicated in BRCA1- and BRCA2-mediated tumor suppression as well as cellular viability, we have begun a functional analysis of a defined RAD51 mutation in mammalian cells. By using a dominant negative approach, we generated a mouse embryonic stem cell line that expresses an ATP hydrolysis-defective RAD51 protein, hRAD51-K133R, at comparable levels to the endogenous wild-type RAD51 protein, whose expression is retained in these cells. We found that these cells have increased sensitivity to the DNA-damaging agents mitomycin C and ionizing radiation and also exhibit a decreased rate of spontaneous sister-chromatid exchange. By using a reporter for the repair of a single chromosomal double-strand break, we also found that expression of the hRAD51-K133R protein specifically inhibits homology-directed double-strand break repair. Furthermore, expression of a BRC repeat from BRCA2, a peptide inhibitor of an early step necessary for strand exchange, exacerbates the inhibition of homology-directed repair in the hRAD51-K133R expressing cell line. Thus, ATP hydrolysis by RAD51 has a key role in various types of DNA repair in mammalian cells.

Purpose: We conducted a randomized Phase II trial to directly compare toxicity, feasibility, and delivered dose intensities of two adjuvant dose-intensive regimens containing doxorubicin, paclitaxel, and cyclophosphamide for patients with node-positive breast carcinoma., Experimental Design: Forty-two patients with resected breast carcinoma involving one or more ipsilateral axillary lymph nodes, were randomized to receive two different schedules of adjuvant chemotherapy using 14-day dosing intervals: either (a) three cycles of doxorubicin 80 mg/m(2) as i.v. bolus followed sequentially by three cycles of paclitaxel 200 mg/m(2) as a 24-h infusion and then by three cycles of cyclophosphamide 3.0 g/m(2) as a 1-h infusion (arm A); or (b) the same schedule of doxorubicin followed by three cycles of concurrent cyclophosphamide and paclitaxel at the same doses (arm B). All cycles were supported by granulocyte colony-stimulating factor administration., Results: Forty-one patients were assessable for toxicity and feasibility; 37 (90%) completed all planned chemotherapy. There was no treatment-related mortality; however, increased toxicity was observed on arm B compared with arm A, manifested by an increase in hospitalization for toxicity, mainly neutropenic fever, and an increased incidence of transfusion of packed RBCs transfusions for anemia. The mean delivered dose intensities for paclitaxel and cyclophosphamide were significantly greater for arm A compared with arm B (P =.01 and P =.05, respectively). There is no long-term, treatment-related toxicity, and no cases of acute myelogenous leukemia or myelodysplastic syndrome have been observed., Conclusions: Dose-dense sequential single-agent chemotherapy is more feasible than doxorubicin with subsequent concurrent paclitaxel and cyclophosphamide.

The establishment of connections between biochemical defects and clinical disease is a major goal of modern molecular genetics. In this review, we examine the current literature that relates defects in the two major DNA double-strand-break repair pathways--homologous recombination and nonhomologous end-joining--with the development of human tumors. Although definitive proof has yet to be obtained, the current literature is highly suggestive of such a link.

Chromosomal breaks occur spontaneously as a result of normal DNA metabolism and after exposure to DNA-damaging agents. A major pathway involved in chromosomal double-strand break repair is homologous recombination. In this pathway, a DNA sequence with similarity to a damaged chromosome directs the repair of the damage. The protein products of the hereditary breast cancer susceptibility genes, BRCA1 and BRCA2, interact with the Rad51 protein, a central component of homologous repair pathways. We have recently shown that this interaction is significant by demonstrating that Brca1- and BRCA2-deficient cells are defective in homology-directed chromosomal break repair. We confirm that Brca1-deficient embryonic stem (ES) cells are defective in gene targeting and homology-directed repair of an I-Sce I-induced chromosome break. The phenotypic paradigm that defines homology-directed repair mutants is extended to these Brca1-deficient cells by the demonstration of 100-fold sensitivity to the interstrand cross-linking agent mitomycin-C and spontaneous chromosome instability. Interestingly, although chromosome aberrations were evident, aneuploidy was not observed. Repair phenotypes are partially restored by expression of a Brca1 transgene, whereas correction of one mutated Brca1 allele through gene targeting fully restores mitomycin-C resistance and chromosome stability. We conclude that the inability to properly repair strand breaks by homology-directed repair gives rise to defects in chromosome maintenance that promote genetic instability and, it is likely, tumorigenesis.

Purpose: This phase II study evaluated weekly trastuzumab and paclitaxel therapy in women with HER2-normal and HER2-overexpressing metastatic breast cancer. Efficacy was correlated with immunohistochemical and fluorescent in situ hybridization (FISH) assay results., Patients and Methods: Eligible patients had bidimensionally measurable metastatic breast cancer. Up to three prior chemotherapy regimens, including prior anthracycline and taxane therapy, were allowed. Trastuzumab 4 mg/kg and paclitaxel 90 mg/m2 were administered on week 1, with trastuzumab 2 mg/kg and paclitaxel 90 mg/m2 administered on subsequent weeks. HER2 status was evaluated using four different immunohistochemical assays and FISH., Results: Patients received a median of 25 weekly infusions (range, one to 85 infusions). Median delivered paclitaxel dose-intensity was 82 mg/m2/wk (range, 52 to 90 mg/m2/wk). The intent-to-treat response rate for all 95 patients enrolled was 56.8% (95% confidence interval, 47% to 67%). A response rate of 61.4% (4.5% complete response, 56.8% partial response) was observed in 88 fully assessable patients. In patients with HER2-overexpressing tumors, overall response rates ranged from 67% to 81% compared with 41% to 46% in patients with HER2-normal expression (ranges reflect the different assay methods used to assess HER2 status). Differences in response rates between patients with HER2-overexpressing tumors and those with normal HER2 expression were statistically significant for all assay methods, with CB11 and TAB250 antibodies and FISH having the strongest significance. Therapy was generally well tolerated, although three patients had serious cardiac complications., Conclusion: Weekly trastuzumab and paclitaxel therapy is active in women with metastatic breast cancer. Therapy was relatively well tolerated; however, attention to cardiac function is necessary.

The BRCA2 tumor suppressor has been implicated in the maintenance of chromosomal stability through a function in DNA repair. In this report, we examine human and mouse cell lines containing different BRCA2 mutations for their ability to repair chromosomal breaks by homologous recombination. Using the I-SceI endonuclease to introduce a double-strand break at a specific chromosomal locus, we find that BRCA2 mutant cell lines are recombination deficient, such that homology-directed repair is reduced 6- to >100-fold, depending on the cell line. Thus, BRCA2 is essential for efficient homology-directed repair, presumably in conjunction with the Rad51 recombinase. We propose that impaired homology-directed repair caused by BRCA2 deficiency leads to chromosomal instability and, possibly, tumorigenesis, through lack of repair or misrepair of DNA damage.

Germline mutations in BRCA1 confer a high risk of breast and ovarian tumors. The role of BRCA1 in tumor suppression is not yet understood, but both transcription and repair functions have been ascribed. Evidence that BRCA1 is involved in DNA repair stems from its association with RAD51, a homolog of the yeast protein involved in the repair of DNA double-strand breaks (DSBs) by homologous recombination. We report here that Brca1-deficient mouse embryonic stem cells have impaired repair of chromosomal DSBs by homologous recombination. The relative frequencies of homologous and nonhomologous DNA integration and DSB repair were also altered. The results demonstrate a caretaker role for BRCA1 in preserving genomic integrity by promoting homologous recombination and limiting mutagenic nonhomologous repair processes.

Motivated by the observation of preclinical synergy, a Phase I dose escalation study of edatrexate in combination with a 3-h paclitaxel infusion was performed in patients with advanced breast cancer to determine the maximum tolerated dose (MTD) of edatrexate and the toxicities associated with this combination and to report preliminary observations of efficacy with this novel combination. Thirty-six patients were enrolled in this Phase I trial. Thirty-five eligible patients were treated every 21 days in cohorts of at least three patients and were assessable for toxicity. One patient was ineligible due to hyperbilirubinemia. Stepwise dose escalations of edatrexate were administered until grade >3 nonhematological dose-limiting toxicities were reported. The initial dose level of edatrexate was 180 mg/m2; subsequent cohorts were treated with escalating doses of edatrexate (210, 240, 270, 300, 350, and 400 mg/m2). Edatrexate was administered by i.v. infusion over 1 h. Paclitaxel was administered 24 h later at a fixed dose of 175 mg/m2 as a 3-h infusion with standard dexamethasone, diphenhydramine, and cimetidine premedication. The MTD of edatrexate was reached at the 350 mg/m2 level in this study. Grade 3 diarrhea was seen in one patient at the 300 and 400 mg/m2 dose levels, requiring dose reductions. Two patients experienced grade 4 stomatitis at the 400 mg/m2 dose level and also required dose reduction, establishing the MTD as 350 mg/m2. Grade 3 nausea and vomiting were noted in two of three patients at the highest dose level. Of 35 patients, 4 patients reported grade 3 myalgias and 1 patient reported grade 3 neurosensory complaints, which were seen mostly at the 350 and 400 mg/m2 dose levels; however, 1 patient reported grade 3 myalgias at 180 mg/m2. No cumulative neurotoxicity was observed, and no patient experienced an allergic reaction to paclitaxel. In 23 patients with bidimensionally measurable disease, there were four complete (17%) and seven partial responses, with an overall response rate of 48% (95% confidence interval, 27-69%). All of the responses were seen in patients who had not received prior chemotherapy for stage IV disease. The median duration of response was not assessable because many responding patients went on to receive high-dose chemotherapy treatment with stem cell support. The combination of edatrexate and paclitaxel for treatment of metastatic breast cancer is a feasible and safe regimen. The MTD of edatrexate was 350 mg/m2 when combined with a 3-h infusion of paclitaxel (175 mg/m2) given 24 h later. Activity was noted even among patients who had relapsed shortly after receiving methotrexate- and/or doxorubicin-containing adjuvant regimens. Additional studies evaluating the sequences and dosing schema for this combination are warranted to improve the response proportion and define the duration of the response.