Capivasertib Plus Fulvestrant vs. Fulvestrant in Primary High-risk Lobular Breast Cancer

The evaluation of CCCA in the HR+/HER2- invasive lobular breast cancer patient population allows assessment of treatment efficacy with an achievable sample size of HR+/HER2- breast cancer patients within an acceptable and scientifically meaningful duration of recruitment. CCCA can be assessed immediately after last patients end of treatment. Central blinded pathological assessment of CCCA is planned in this study as a standardized preparation of the sampled tissue by the central pathologist. This pathologist is blinded regarding the study therapy administered, i. e. with or without capivasertib. The addition of capivasertib to fulvestrant in many clinical trials correlates with an improvement in PFS compared to fulvestrant alone in patients with HR+/HER2- locally advanced or metastatic breast cancer. This effect was observed regardless of a PI3K/AKT/mTOR pathway activation. None of the ongoing studies investigate the effects of the combined treatment in invasive lobular breast cancer. Given that these tumors are less likely to respond to chemotherapy, identification of patients that can be spared from chemotherapy is desirable. On the other hand, it is important to identify patients with invasive lobular breast cancer not responding to neoadjuvant ET who might be at increased risk for recurrence, who would therefore potentially benefit from further adjuvant therapies including chemotherapy. Given the high rates of PI3K pathway alterations in such tumors, it is expected that the CCCA rate could be increased by adding capivasertib to fulvestrant. GBG expect that the potential benefit of improved CCCA rate with a combination treatment compared to fulvestrant monotherapy would outweigh the potential risks due to added toxicity, which has already been shown in clinical trials to be well tolerated by patients.