Efficacy of everolimus-containing chemotherapy in HER2 negative metastatic breast cancer patients with PI3K/AKT/mTOR mutations: A retrospective study

e13069 Background: The PI3K/AKT/mTOR pathway is frequently altered in breast cancer. Everolimus is a selective inhibitor of mammalian target of Rapamycin (mTOR).The benefit of everolimus in metastatic breast cancer patients with PI3K/AKT/mTOR mutations remains unclear, especially in TNBC patients. Our study aimed to investigate the efficacy of the everolimus-containing chemotherapy in metastatic breast cancer patients with PI3K/AKT/mTOR mutations. Methods: 13 cases of HER2- metastatic breast cancer with PI3K/AKT/mTOR mutations treated with everolimus-containing chemotherapy were analyzed. The genetic profile in PI3K/AKT/mTOR pathway was studied. Results: Overall, 4 cases were hormone receptor (HR) positive and 9 were TNBC. 7 patients only had PIK3CA mutations, 1 patient had only PIK3R1 mutations, and 5 patients had other mutations in the pathway in addition to PIK3CA, including PTEN, PIK3CB, CTNNB1, FGFR1 and TSC2. 5 cases were treated as first or second line chemotherapy, and 8 were as third line or above. The ORR (CR+PR) was 38.5% (5/13), and DCR (CR+PR+SD) was 84.6% (11/13), including 5 cases of PR, 6 cases of SD, and 2 cases of PD. The median PFS was 5.8 months (95% CI 3.7-9.7), and the median OS was 14.3 months (95% CI 6.47-null). However, the ORR of TNBC patients was higher than that of HR-positive, which were 44.4% (4/9) and 25% (1/4), respectively ( p = 0.070). The mPFS was also longer than that of HR-positive with 5.8 months versus 1.7 months, as well as the mOS with 14.3 versus 3.8 months. We also found that the patients carrying other mutations besides PIK3CA in the PI3K/AKT/mTOR pathway had a longer PFS compared to the patients without other mutations, which was 9.7 months and 4.3 months respectively ( p = 0.272). And the DCR of the two groups were 100% and 75% respectively ( p = 0.451). Conclusions: We found that everolimus-containing chemotherapy was effective in the treatment of HER2- metastatic breast cancer with PI3K/AKT/mTOR pathway activation. TNBC patients had a trend of longer mPFS than HR+ patients. And the patients carrying other mutations besides PIK3CA in the PI3K/AKT/mTOR pathway have a trend of longer PFS and higher DCR compared to the patients without other mutations. However, trails with larger samples are needed for further verification.