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Purpose: Long-term outcomes of patients with stage I human epidermal growth factor receptor 2 (HER2)-positive breast cancer receiving adjuvant trastuzumab emtansine (T-DM1) remain undefined, and prognostic predictors represent an unmet need., Methods: In the ATEMPT phase II trial, patients with stage I centrally confirmed HER2-positive breast cancer were randomly assigned 3:1 to adjuvant T-DM1 for 1 year or paclitaxel plus trastuzumab (TH). Coprimary objectives were to compare the incidence of clinically relevant toxicities between arms and to evaluate invasive disease-free survival (iDFS) with T-DM1. Correlative analyses included the HER2DX genomic tool, multiomic evaluations of HER2 heterogeneity, and predictors of thrombocytopenia., Results: After a median follow-up of 5.8 years, 11 iDFS events were observed in the T-DM1 arm, consistent with a 5-year iDFS of 97.0% (95% CI, 95.2 to 98.7). At 5 years, the recurrence-free interval (RFI) was 98.3% (95% CI, 97.0 to 99.7), the overall survival was 97.8% (95% CI, 96.3 to 99.3), and the breast cancer-specific survival was 99.4% (95% CI, 98.6 to 100). Comparable iDFS was observed with T-DM1 irrespective of tumor size, hormone receptor status, centrally determined HER2 immunohistochemical score, and receipt of T-DM1 for more or less than 6 months. Although ATEMPT was not powered for this end point, the 5-year iDFS in the TH arm was 91.1%. Among patients with sufficient tissue for HER2DX testing (n = 187), 5-year outcomes significantly differed according to HER2DX risk score, with better RFI (98.1% v 81.8%, hazard ratio [HR], 0.10, P = .01) and iDFS (96.3% v 81.8%, HR, 0.20, P = .047) among patients with HER2DX low-risk versus high-risk tumors, respectively., Conclusion: Adjuvant T-DM1 for 1 year leads to outstanding long-term outcomes for patients with stage I HER2-positive breast cancer. A high HER2DX risk score predicted a higher risk of recurrence in ATEMPT.

Purpose: The ATEMPT trial was designed to determine if treatment with trastuzumab emtansine (T-DM1) caused less toxicity than paclitaxel plus trastuzumab (TH) and yielded clinically acceptable invasive disease-free survival (iDFS) among patients with stage I human epidermal growth factor receptor 2-positive (HER2+) breast cancer (BC)., Methods: Patients with stage I centrally confirmed HER2+ BC were randomly assigned 3:1 to T-DM1 or TH and received T-DM1 3.6 mg/kg IV every 3 weeks for 17 cycles or T 80 mg/m 2 IV with H once every week × 12 weeks (4 mg/kg load →2 mg/kg), followed by H × 39 weeks (6 mg/kg once every 3 weeks). The co-primary objectives were to compare the incidence of clinically relevant toxicities (CRTs) in patients treated with T-DM1 versus TH and to evaluate iDFS in patients receiving T-DM1., Results: The analysis population includes all 497 patients who initiated protocol therapy (383 T-DM1 and 114 TH). CRTs were experienced by 46% of patients on T-DM1 and 47% of patients on TH ( P = .83). The 3-year iDFS for T-DM1 was 97.8% (95% CI, 96.3 to 99.3), which rejected the null hypothesis ( P < .0001). Serially collected patient-reported outcomes indicated that patients treated with T-DM1 had less neuropathy and alopecia and better work productivity compared with patients on TH., Conclusion: Among patients with stage I HER2+ BC, one year of adjuvant T-DM1 was associated with excellent 3-year iDFS, but was not associated with fewer CRT compared with TH., Competing Interests: Sara TolaneyConsulting or Advisory Role: Novartis, Pfizer, Merck, Lilly, Nektar, NanoString Technologies, AstraZeneca, Puma Biotechnology, Genentech, Eisai, Sanofi, Celldex, Bristol Myers Squibb, Paxman, Seattle Genetics, Odonate Therapeutics, AbbVie, Silverback Therapeutics, G1 Therapeutics, OncoPep, Kyowa Hakko Kirin, Samsung Bioepis, CytomX Therapeutics, Daiichi Sankyo, Athenex, Immunomedics/Gilead, Mersana, CertaraResearch Funding: Genentech/Roche, Merck, Exelixis, Pfizer, Lilly, Novartis, Bristol Myers Squibb, Eisai, AstraZeneca, NanoString Technologies, Cyclacel, Nektar, Immunomedics, Odonate Therapeutics, Sanofi, Seattle GeneticsTravel, Accommodations, Expenses: AstraZeneca, Lilly, Merck, Nektar, Novartis, Pfizer, Genentech/Roche, Immunomedics, Eisai, NanoString Technologies, Puma Biotechnology, Celldex Chau DangHonoraria: Puma Biotechnology, eviCore healthcareConsulting or Advisory Role: Puma Biotechnology, eviCore healthcareResearch Funding: Genentech/Roche, Puma Biotechnology Denise YardleyConsulting or Advisory Role: Novartis, Biotheranostics, Bristol Myers Squibb, G1 Therapeutics, Athenex, Immunomedics, Sanofi/Aventis, R-Pharm, LillySpeakers' Bureau: Novartis, Genentech/Roche, Genentech/RocheResearch Funding: Genentech/Roche, Novartis, MedImmune, Lilly, Medivation, Pfizer, Tesaro, Macrogenics, AbbVie, Merck, Clovis Oncology, Amgen, Biomarin, Biothera, Dana Farber Cancer Hospital, Incyte, Innocrin Pharma, Nektar, NSABP Foundation, Odonate Therapeutics, PolyphorTravel, Accommodations, Expenses: Novartis, Genentech/Roche Steven IsakoffConsulting or Advisory Role: AbbVie, OncoPep, Puma Biotechnology, Seattle Genetics, NovartisResearch Funding: Genentech, PharmaMar, AbbVie, OncoPep, Merck, AstraZeneca/MedImmune, Outcomes4Me Vicente ValeroHonoraria: Genentech/Roche, Merck, NovartisConsulting or Advisory Role: Genentech/Roche, Novartis, MerckTravel, Accommodations, Expenses: Genentech/Roche Therese MulveyConsulting or Advisory Role: Outcomes4Me Ron BoseConsulting or Advisory Role: GenentechResearch Funding: Puma Biotechnology Antonio WolffConsulting or Advisory Role: Ionis PharmaceuticalsResearch Funding: Biomarin, CelldexPatents, Royalties, Other Intellectual Property: Antonio Wolff has been named as inventor on one or more issued patents or pending patent applications related to methylation in breast cancer and has assigned his rights to JHU and participates in a royalty sharing agreement with JHUOpen Payments Link: https://openpaymentsdata.cms.gov/physician/357301/summary Katherine Reeder-HayesResearch Funding: Pfizer Hope RugoHonoraria: Puma Biotechnology, MylanConsulting or Advisory Role: SamsungResearch Funding: Macrogenics, OBI Pharma, Eisai, Pfizer, Novartis, Lilly, Genentech, Merck, Immunomedics, Odonate Therapeutics, Daiichi Sankyo, Seattle Genetics, Sermonix Pharmaceuticals, AstraZenecaTravel, Accommodations, Expenses: Pfizer, Novartis, Macrogenics, Mylan, Daiichi Sankyo, AstraZeneca Spain, MerckOpen Payments Link: https://openpaymentsdata.cms.gov/summary Bhuvaneswari RamaswamyConsulting or Advisory Role: Eisai Lowell HartHonoraria: Novartis, Daiichi Sankyo, AstraZeneca, Seattle Genetics, G1 Therapeutics, Veracyte, Karyopharm TherapeuticsConsulting or Advisory Role: Genentech/Roche, Amgen, G1 Therapeutics, Merck, Seattle GeneticsSpeakers' Bureau: Bristol Myers Squibb, Lilly, Pfizer, Genentech, AstraZeneca, NovartisResearch Funding: Novartis, Genentech/Roche, Bristol Myers Squibb, G1 Therapeutics, Seattle Genetics Vijayakrishna GadiLeadership: SEngine Precision MedicineStock and Other Ownership Interests: Sengine precision medicine, Novilla, 3rdEyeBio, New Equilibrium BiosciencesConsulting or Advisory Role: Seattle Genetics, Puma Biotechnology, Novartis, SanofiSpeakers' Bureau: Seagen, bioTheranosticsResearch Funding: Genentech/Roche, SignalOne Bio, AgendiaTravel, Accommodations, Expenses: NovartisOpen Payments Link: https://openpaymentsdata.cms.gov/physician/2511 Bryan SchneiderHonoraria: Lilly, Research to Practice Paul MarcomConsulting or Advisory Role: Genentech/Roche, ImmunomedicsResearch Funding: Novartis, Genentech/Roche, AstraZeneca, Verily, Glycomimetics, MillenniumOpen Payments Link: https://openpaymentsdata.cms.gov/physician/237508/summary Kathy AlbainConsulting or Advisory Role: Novartis, Pfizer, Myriad Genetics, Genomic Health, Agendia, Genentech/RocheResearch Funding: Seattle GeneticsOther Relationship: Puma Biotechnology Nadine TungResearch Funding: AstraZeneca Rita NandaConsulting or Advisory Role: Merck, Genentech/Roche, Pfizer, Macrogenics, Daiichi Sankyo, Athenex, Aduro Biotech, ION Pharma, Seattle Genetics, ImmunomedicsResearch Funding: Corcept Therapeutics, Celgene, Merck, Seattle Genetics, Genentech/Roche, Odonate Therapeutics, Pfizer, AstraZeneca, AbbVie, ImmunomedicsOther Relationship: G1 Therapeutics Rachel JankowitzHonoraria: EisaiConsulting or Advisory Role: Merck Mothaffar RimawiConsulting or Advisory Role: Macrogenics, Daiichi Sankyo, Seattle Genetics, GenentechResearch Funding: Pfizer Vandana AbramsonEmployment: HCA HealthcareConsulting or Advisory Role: Eisai, Daiichi Sankyo, AbbvieResearch Funding: Genentech/Roche, Lilly Paula PohlmannLeadership: Immunonet BioSciencesStock and Other Ownership Interests: Immunonet BioSciencesHonoraria: Dava Oncology, OncLive/MJH Life Sciences, Frontiers—PublisherConsulting or Advisory Role: Personalized Cancer Therapy, OncoPlex Diagnostics, Immunonet BioSciences, Pfizer, HERON, Puma Biotechnology, Sirtex Medical, Caris Life Sciences, Juniper Pharmaceuticals, Bolt BiotherapeuticsSpeakers' Bureau: Genentech/RocheResearch Funding: Genentech/Roche, Fabre-Kramer, Advanced Cancer Therapeutics, Caris Centers of Excellence, Pfizer, Pieris Pharmaceuticals, Cascadian Therapeutics, Bolt Biotherapeutics, Byondis, SeagenPatents, Royalties, Other Intellectual Property: United States Patent no. 8486413, United States Patent no. 8501417, United States Patent no. 9023362, United States Patent no. 9745377, Patent application Catherine Van PoznakResearch Funding: BayerPatents, Royalties, Other Intellectual Property: UpToDate Andres Forero-TorresEmployment: Seattle GeneticsStock and Other Ownership Interests: Seattle Genetics Minetta LiuResearch Funding: Eisai, Seattle Genetics, Novartis, Roche/Genentech, GRAIL, Merck, Tesaro, Menarini Silicon Biosystems, Genomic HealthTravel, Accommodations, Expenses: GRAIL, Merck, Menarini Silicon Biosystems, Pfizer, Genomic Health, AstraZeneca, Ionis Pharmaceuticals Kathryn RuddyPatents, Royalties, Other Intellectual Property: My husband is a co-inventor of technology licensed by Mayo Clinic to AliveCor (MountainView, CA), which makes a smartphone-enabled remote ECG monitoring system Richard GelberResearch Funding: AstraZeneca, Novartis, Roche, Merck, PfizerTravel, Accommodations, Expenses: Roche, AstraZeneca, Novartis Bill BarryEmployment: Rho Ann PartridgePatents, Royalties, Other Intellectual Property: I receive small royalty payments for co-authoring the breast cancer survivorship section of UpToDateTravel, Accommodations, Expenses: Novartis Eric WinerHonoraria: Genentech/Roche, Genomic HealthConsulting or Advisory Role: Leap Therapeutics, Seattle Genetics, Jounce Therapeutics, GlaxoSmithKline, Carrick Therapeutics, Lilly, G1 Therapeutics, Syros Pharmaceuticals, Genentech/Roche, Gilead Sciences, Zymeworks, AthenexResearch Funding: GenentechOther Relationship: InfiniteMD Ian KropEmployment: AMAG Pharmaceuticals, Freeline TherapeuticsLeadership: AMAG Pharmaceuticals, Freeline TherapeuticsStock and Other Ownership Interests: AMAG Pharmaceuticals, Freeline Therapeutics, VertexHonoraria: Genentech/Roche, AstraZeneca, CelltrionConsulting or Advisory Role: Genentech/Roche, Seattle Genetics, Daiichi Sankyo, Macrogenics, Taiho Pharmaceutical, Context Therapeutics, Novartis, Merck, Ionis Pharmaceuticals, Bristol Myers Squibb, AstraZenecaResearch Funding: Genentech, PfizerNo other potential conflicts of interest were reported.

Purpose: Predictive biomarkers to identify patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer who may benefit from targeted therapy alone are required. We hypothesized that early measurements of tumor maximum standardized uptake value corrected for lean body mass (SULmax) on 18 F-labeled fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) would predict pathologic complete response (pCR) to pertuzumab and trastuzumab (PT)., Patients and Methods: Patients with stage II or III, estrogen receptor-negative, HER2-positive breast cancer received four cycles of neoadjuvant PT. 18 F-labeled fluorodeoxyglucose positron emission tomography-computed tomography was performed at baseline and 15 days after PT initiation (C1D15). Eighty evaluable patients were required to test the null hypothesis that the area under the curve of percent change in SULmax by C1D15 predicting pCR is ≤ 0.65, with a one-sided type I error rate of 10%., Results: Eighty-eight women were enrolled (83 evaluable), and 85% (75 of 88) completed all four cycles of PT. pCR after PT alone was 22%. Receiver operator characteristic analysis of percent change in SULmax by C1D15 yielded an area under the curve of 0.72 (80% CI, 0.64 to 0.80; one-sided P = .12), which did not reject the null hypothesis. However, between patients who obtained pCR and who did not, a significant difference in median percent reduction in SULmax by C1D15 was observed (63.8% v 41.8%; P = .004) and SULmax reduction ≥ 40% was more prevalent (83% v 52%; P = .03; positive predictive value, 31%). Participants not obtaining a 40% reduction in SULmax by C1D15 were unlikely to obtain pCR (negative predictive value, 91%)., Conclusion: Although the primary objective was not met, early changes in SULmax predict response to PT in estrogen receptor-negative and HER2-positive breast cancer. Once optimized, this quantitative imaging strategy may facilitate tailoring of therapy in this setting., Competing Interests: Roisin M. ConnollyResearch Funding: Genentech/Roche, Puma Biotechnology, Novartis, Merck, MacrogenicsOther Relationship: Pfizer Lilja SolnesConsulting or Advisory Role: ProgenicsResearch Funding: AAA/Novartis, Progenics Vandana AbramsonEmployment: HCA HealthcareConsulting or Advisory Role: Eisai, Daiichi Sankyo, AbbvieResearch Funding: Genentech/Roche, Lilly Lisa A. CareyResearch Funding: Innocrin Pharma, Syndax, Immunomedics, Novartis, NanoString Technologies, Abbvie, Seattle GeneticsPatents, Royalties, Other Intellectual Property: Royalty-sharing agreement, investorship interest in licensed IP to startup company, Falcon Therapeutics, that is designing neural stem cell-based therapy for glioblastoma multiformeUncompensated Relationships: Sanofi, Novartis, G1 Therapeutics, Genentech/Roche, GlaxoSmithKline, Exact Sciences, AstraZeneca/Daiichi Sankyo, Aptitude HealthOpen Payments Link: https://openpaymentsdata.cms.gov/physician/179671 Minetta C. LiuResearch Funding: Eisai, Seattle Genetics, Novartis, Roche/Genentech, GRAIL, Merck, Tesaro, Menarini Silicon Biosystems, Genomic HealthTravel, Accommodations, Expenses: Grail, Merck, Menarini Silicon Biosystems, Pfizer, Genomic Health, AstraZeneca, Ionis Pharmaceuticals Mothaffar RimawiConsulting or Advisory Role: Macrogenics, Daiichi Sankyo, Seattle Genetics, GenentechResearch Funding: Pfizer Jennifer SpechtHonoraria: Nektar, Genomic Health, Daiichi SankyoConsulting or Advisory Role: Genomic Health, Nektar, Daiichi SankyoResearch Funding: Pfizer, Nektar, Merck, Myriad Pharmaceuticals, Cascadian Therapeutics, Pfizer, Minerva Biotechnologies, Seattle Genetics, Novartis, Chalasani, Xencor, Johns Hopkins University, Genentech, Dana-Farber Cancer Institute, NCITravel, Accommodations, Expenses: Nektar Anna Maria StornioloEmployment: Sophren Therapeutics, Q32Bio IncLeadership: Sophren Therapeutics, Q32Bio IncStock and Other Ownership Interests: Gilead Sciences, Moderna Therapeutics, Merck, Lilly, Gilead, Pfizer, Meridian Bioscience IncConsulting or Advisory Role: Q32bio, Tri-I TDI, Deerfield Management, Atlas Venture, Boston PharmaceuticalsResearch Funding: QUE Oncology, Pfizer Vicente ValeroHonoraria: Genentech/Roche, Merck, NovartisConsulting or Advisory Role: Genentech/Roche, Novartis, MerckTravel, Accommodations, Expenses: Genentech/Roche Christos VaklavasEmployment: Flatiron HealthHonoraria: Guidepoint GlobalConsulting or Advisory Role: Daiichi SankyoResearch Funding: Genentech, Roche, Pfizer, Incyte, Pharmacyclics, Novartis, TRACON Pharma, Innocrin Pharma, Zymeworks, H3 BiomedicineOther Relationship: Puma Biotechnology, Takeda, Daiichi SankyoUncompensated Relationships: GenentechOpen Payments Link: https://openpaymentsdata.cms.gov/physician/1306968 Ian E. KropEmployment: AMAG Pharmaceuticals, Freeline TherapeuticsLeadership: AMAG Pharmaceuticals, Freeline TherapeuticsStock and Other Ownership Interests: AMAG Pharmaceuticals, Freeline Therapeutics, VertexHonoraria: Genentech/Roche, AstraZeneca, CelltrionConsulting or Advisory Role: Genentech/Roche, Seattle Genetics, Daiichi Sankyo, Macrogenics, Taiho Pharmaceutical, Context Therapeutics, Novartis, Merck, Ionis Pharmaceuticals, Bristol Myers Squibb, AstraZenecaResearch Funding: Genentech, Pfizer Eric P. WinerHonoraria: Genentech/Roche, Genomic HealthConsulting or Advisory Role: Leap Therapeutics, Seattle Genetics, Jounce Therapeutics, GlaxoSmithKline, Carrick Therapeutics, Lilly, G1 Therapeutics, Syros Pharmaceuticals, Genentech/Roche, Gilead Sciences, ZymeworksResearch Funding: Genentech, AstraZenecaOther Relationship: InfiniteMD Antonio C. WolffConsulting or Advisory Role: Ionis PharmaceuticalsResearch Funding: Biomarin, CelldexPatents, Royalties, Other Intellectual Property: Antonio Wolff has been named as inventor on one or more issued patents or pending patent applications relating to methylation in breast cancer, and has assigned his rights to JHU, and participates in a royalty sharing agreement with JHUOpen Payments Link: https://openpaymentsdata.cms.gov/physician/357301/summary Ashley Cimino-MathewsEmployment: Vivante HealthHonoraria: Bristol Myers Squibb, RocheResearch Funding: Bristol Myers Squibb Ben H. ParkLeadership: LoxoStock and Other Ownership Interests: Loxo, CelcuityHonoraria: AstraZenecaConsulting or Advisory Role: Horizon Discovery, Foundation Medicine, Loxo, Casdin Capital, H3 Biomedicine, Jackson Laboratory for Genomic Medicine, Lilly, Celcuity, Sermonix Pharmaceuticals, PathovaxResearch Funding: Abbvie, Pfizer, GE Healthcare, LillyPatents, Royalties, Other Intellectual Property: Royalties paid through inventions at Johns Hopkins University by Horizon Discovery LtdTravel, Accommodations, Expenses: Lilly, LoxoUncompensated Relationships: Tempus Richard L. WahlStock and Other Ownership Interests: ProgenicsHonoraria: Siemens Healthineers, Bristol Myers Squibb, Jubilant DraxImage, Actinium Medical Advisory BoardConsulting or Advisory Role: Clarity PharmaceuticalsResearch Funding: Whiterabbit AI, Siemens Healthineers, Bristol Myers Squibb, Actinium PharmaceuticalsTravel, Accommodations, Expenses: Siemens Healthineers, Actinium PharmaceuticalsOther Relationship: Society of Nuclear Medicine Vered StearnsResearch Funding: Abbvie, Pfizer, Novartis, Puma Biotechnology, BioceptOther Relationship: ImmunomedicsNo other potential conflicts of interest were reported.

Purpose: Predictive biomarkers to identify patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer who may benefit from targeted therapy alone are required. We hypothesized that early measurements of tumor maximum standardized uptake values corrected for lean body mass (SULmax) on [ 18 F]fluorodeoxyglucose positron emission tomography/computed tomography would predict pathologic complete response (pCR) to neoadjuvant pertuzumab and trastuzumab (PT)., Patients and Methods: Patients with stage II/III, estrogen receptor-negative, HER2-positive breast cancer received four cycles of neoadjuvant PT. [ 18 F]Fluorodeoxyglucose positron emission tomography/computed tomography was performed at baseline and 15 days after PT initiation (C1D15). Eighty evaluable patients were required to test the null hypothesis that the area under the curve of percentage of change in SULmax by C1D15 predicting pCR is less than or equal to 0.65, with a one-sided type I error rate of 10%., Results: Eighty-eight women were enrolled (83 evaluable), and 85% (75 of 88) completed all four cycles of PT. pCR after PT alone was 34%. Receiver operating characteristic analysis yielded an area under the curve of 0.76 (90% CI, 0.67 to 0.85), which rejected the null hypothesis. Between patients who obtained pCR versus not, a significant difference in median percent reduction in SULmax by C1D15 was observed (63.8% v 33.5%; P < .001), an SULmax reduction greater than or equal to 40% was more prevalent (86% v 46%; P < .001; negative predictive value, 88%; positive predictive value, 49%), and a significant difference in median C1D15 SULmax (1.6 v 3.9; P < .001) and higher proportion of C1D15 SULmax less than or equal to 3 (93% v 38%; P < .001; negative predictive value, 94%; positive predictive value, 55%) were observed., Conclusion: Early changes in SULmax predict response to four cycles of PT in estrogen receptor-negative, HER2-positive breast cancer. Once optimized, this quantitative imaging strategy may facilitate a more tailored approach to therapy in this setting.

Purpose: CDK4/6 inhibitors are used to treat estrogen receptor (ER)-positive metastatic breast cancer (BC) in combination with endocrine therapy. PALLET is a phase II randomized trial that evaluated the effects of combination palbociclib plus letrozole as neoadjuvant therapy., Patients and Methods: Postmenopausal women with ER-positive primary BC and tumors greater than or equal to 2.0 cm were randomly assigned 3:2:2:2 to letrozole (2.5 mg/d) for 14 weeks (A); letrozole for 2 weeks, then palbociclib plus letrozole to 14 weeks (B); palbociclib for 2 weeks, then palbociclib plus letrozole to 14 weeks (C); or palbociclib plus letrozole for 14 weeks. Palbociclib 125 mg/d was administered orally on a 21-days-on, 7-days-off schedule. Core-cut biopsies were taken at baseline and 2 and 14 weeks. Coprimary end points for letrozole versus palbociclib plus letrozole groups (A v B + C + D) were change in Ki-67 (protein encoded by the  MKI67 gene; immunohistochemistry) between baseline and 14 weeks and clinical response (ordinal and ultrasound) after 14 weeks. Complete cell-cycle arrest was defined as Ki-67 less than or equal to 2.7%. Apoptosis was characterized by cleaved poly (ADP-ribose) polymerase., Results: Three hundred seven patients were recruited. Clinical response was not significantly different between palbociclib plus letrozole and letrozole groups ( P = .20; complete response + partial response, 54.3% v 49.5%), and progressive disease was 3.2% versus 5.4%, respectively. Median log-fold change in Ki-67 was greater with palbociclib plus letrozole compared with letrozole (-4.1 v -2.2; P < .001) in the 190 evaluable patients (61.9%), corresponding to a geometric mean change of -97.4% versus -88.5%. More patients on palbociclib plus letrozole achieved complete cell-cycle arrest (90% v 59%; P < .001). Median log-fold change (suppression) of cleaved poly (ADP-ribose) polymerase was greater with palbociclib plus letrozole versus letrozole (-0.80 v -0.42; P < .001). More patients had grade 3 or greater toxicity on palbociclib plus letrozole (49.8% v 17.0%; P < .001) mainly because of asymptomatic neutropenia., Conclusion: Adding palbociclib to letrozole significantly enhanced the suppression of malignant cell proliferation (Ki-67) in primary ER-positive BC, but did not increase the clinical response rate over 14 weeks, which was possibly related to a concurrent reduction in apoptosis.

Purpose: To assess pertuzumab plus trastuzumab and an aromatase inhibitor (AI) in patients with human epidermal growth factor receptor 2 (HER2)-positive and hormone receptor-positive metastatic/locally advanced breast cancer (MBC/LABC)., Patients and Methods: The PERTAIN trial (NCT01491737) is an ongoing randomized, open-label, multicenter-80 sites and eight countries-phase II trial. Patients have HER2-positive, hormone receptor-positive MBC/LABC and no prior systemic therapy with the exception of endocrine. Random assignment was 1:1 to intravenous pertuzumab (840 mg loading dose followed by 420 mg every 3 weeks) plus trastuzumab (8 mg/kg followed by 6 mg/kg every 3 weeks), and oral anastrozole (1 mg every day) or letrozole (2.5 mg every day), or trastuzumab and an AI. Induction intravenous docetaxel every 3 weeks or paclitaxel every week could be administered for 18 to 24 weeks at the investigator's discretion (decided before but given after random assignment). Primary end point was progression-free survival (PFS). Patients were stratified by whether they received induction chemotherapy and their time since adjuvant hormone therapy., Results: One hundred twenty-nine patients were randomly assigned per arm (February 2012 to October 2014; intent-to-treat populations); 75 in one arm and 71 in the other were chosen to receive induction chemotherapy. Stratified median PFS was 18.89 months (95% CI, 14.09 to 27.66 months) in the pertuzumab plus trastuzumab arm and 15.80 months (95% CI, 11.04 to 18.56 months) in the trastuzumab arm (stratified hazard ratio, 0.65; 95% CI, 0.48 to 0.89; P = .0070). Serious adverse events (AEs) were reported for 42 (33.1%) of 127 and 24 (19.4%) of 124 patients in the safety populations of the pertuzumab plus trastuzumab and trastuzumab arms, respectively. Rates of grade ≥ 3 AEs were 64 (50.4%) of 127 and 48 (38.7%) of 124, respectively. There were no deaths as a result of AEs., Conclusion: PERTAIN met its primary PFS end point. Pertuzumab plus trastuzumab and an AI is effective for the treatment of HER2-positive MBC/LABC. The safety profile was consistent with previous trials of pertuzumab plus trastuzumab.

Purpose: Phosphatase and tensin homolog (PTEN) loss or activating mutations of phosphoinositol-3 (PI3) kinase (PIK3CA) may be associated with trastuzumab resistance. Trastuzumab, the humanized human epidermal growth factor receptor 2 (HER2) monoclonal antibody, and lapatinib, an epidermal growth factor receptor/HER2 tyrosine kinase inhibitor, are both established treatments for HER2-overexpressing breast cancers. Understanding of the cellular response to HER2-targeted therapies is needed to tailor treatments and to identify patients less likely to benefit., Methods: We evaluated the effect of trastuzumab or lapatinib in three HER2-overexpressing cell lines. We confirmed the in vitro observations in two neoadjuvant clinical trials in patients with HER2 overexpression; 35 patients received trastuzumab as a single agent for the first 3 weeks, then docetaxel every 3 weeks for 12 weeks (trastuzumab regimen), whereas 49 patients received lapatinib as a single agent for 6 weeks, followed by trastuzumab/docetaxel for 12 weeks before primary surgery (lapatinib regimen). Apoptosis, Ki67, p-MAPK, p-AKT, and PTEN were assessed by immunohistochemistry. Genomic DNA was sequenced for PIK3CA mutations., Results: Under low PTEN conditions, in vitro data indicate that lapatinib alone and in combination with trastuzumab was effective in decreasing p-MAPK and p-AKT levels, whereas trastuzumab was ineffective. In the clinical trials, we confirmed that low PTEN or activating mutation in PIK3CA conferred resistance to the trastuzumab regimen (P = .015), whereas low PTEN tumors were associated with a high pathologic complete response rate (P = .007)., Conclusion: Activation of PI3 kinase pathway is associated with trastuzumab resistance, whereas low PTEN predicted for response to lapatinib. These observations support clinical trials with the combination of both agents.