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Cancer progression is driven in part by genomic alterations

Trastuzumab deruxtecan (T-DXd) is an anti-HER2 (human epidermal growth factor receptor 2) antibody-drug conjugate which has previously shown efficacy in patients with HER2-overexpressing and HER2-low metastatic breast cancer (mBC). However, the mechanisms of action and resistance of this drug remain partially unclear. DAISY (NCT04132960) is a phase II, open-label study that included patients with mBC whose disease progressed after at least one line of chemotherapy in the metastatic setting. Patients were enrolled in three cohorts according to HER2 expression determined by immunohistochemistry (IHC); cohort 1: HER2-overexpressing (HER2 IHC 3 + or HER2 IHC 2+/ISH+, n = 72), cohort 2: HER2-low (HER2 IHC2+/ISH- or HER2 IHC 1+, n = 74), and cohort 3: HER2 IHC 0 mBC (n = 40). Patients were treated with T-DXd 5.4 mg/kg every 3 weeks until disease progression or unacceptable toxicity. In the full analysis set population (n = 177), the confirmed objective response rate (ORR) was of 70.6% (95% CI: 58.3–81) in cohort 1, 37.5% (95% CI: 26.4–49.7) in cohort 2, and 29.7% (95% CI: 15.9–47) in cohort 3 (p p = 0.007), and cohort 3 with shorter PFS (adjusted HR: 1.96, 95% IC: 1.21–3.15, p = 0.006) as compared to cohort 2. Exploratory analyses showed that HER2 spatial distribution predicted T-DXd response in patients with HER2-overexpressing mBC and that the transcriptomic response to T-DXd was different according to HER2 expression. No quantitative modulation of tumor microenvironment was observed after 6 to 8 weeks of treatment. Finally, recurrent mutations of the DNA repair gene SLX4 were identified in 20% of samples at resistance (4/20) as compared to 2% in baseline samples (2/88), suggesting that SLX4 mutations could mediate secondary resistance to T-DXd. These data suggest that HER2 is a key determinant of T-DXd efficacy. However, an antitumor activity is also observed in a subgroup of patients without detectable HER2 expression and resistance could be partially mediated by payload sensitivity.

The impact of single-agent antibodies against programmed death-ligand 1 (PD-L1) as maintenance therapy is unknown in patients with metastatic breast cancer. The SAFIR02-BREAST IMMUNO substudy included patients with human epidermal growth factor receptor type 2 (Her2)-negative metastatic breast cancer whose disease did not progress after six to eight cycles of chemotherapy. Patients (n = 199) were randomized to either durvalumab (10 mg kg

BACKGROUND: Activating PIK3CA mutations occur in 20-30% of patients with metastatic breast cancer (mBC). A recent study showed that alpha selective PI3K inhibitors improve outcome in patients with PIK3CA mutation, HR+/Her2- mBC. There is a need to better understand the natural history of PIK3CA mutant mBC to optimally position of this drug family. PATIENTS AND METHODS: 649 patients from SAFIR02 trial (NCT02299999), for which mutational profile was available and with clinical data entered in a database, were selected for this analysis. Associations between PIK3CA mutation, clinical characteristics and outcome were analyzed. RESULTS: 143 patients (22%) harbor PIK3CA mutation in tumor sample. 10% (n=27) and 34% (n=104) of TNBC and HR+/Her2- mBC presented a PIK3CA mutation respectively (p CONCLUSION: Patients with PIK3CA mutated, HR+/Her2- mBC are less sensitive to chemotherapy and present a shorter survival. These data emphasize the need for new therapies in this setting, and to position these therapies earlier than chemotherapy in the treatment sequences. Citation Format: Fernanda Mosele, Benjamin Verret, Amelie Lusque, Thomas Filleron, Thomas Bachelot, Monica Arnedos, Mario Campone, Florence Dalenc, Claudia Lefeuvre, Marie Paule Sablin, Hervé Bonnefoi, Ludovic Lacroix, Ivan Bièche, Anthony Gonçalves, William Jacot, Marta Jimenez, Amelie Jacquet, Fabrice Andre, Fabrice Andre. Natural history and outcome of patients presenting a metastatic breast cancer with PIK3CA mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4895.