Prognostic Subset of Metastatic and Non-Metastatic Luminal B Breast Cancer (LBBC) Subtype Based on Ki67 Index.

e12570 Background: Gene expression profiling for breast cancer has classified ER positive subtype into luminal A and luminal B. Luminal B breast cancer (LBBC) have a higher proliferation and poorer prognosis than luminal A tumors. Ki-67 index is the commonly used proliferation marker in breast cancer; however Ki67 expression can also be used to identify a subset of patients among LB with a favorable prognosis. This study attempts to verify this subset of LBBC patients based on DFS and PFS in non-metastatic and metastatic patients respectively. Methods: We retrospectively analyzed 80 IDC breast cancer patients diagnosed in 2013-2016 with complete follow-up till January-2021. We defined LBBC as ER+, PR+ or PR- , HER2+ or HER2- with a Ki67 index >20%. PFS was considered as the endpoint in patients presenting with metastatic disease whereas DFS was used in non-metastatic disease. The cut-off for ki67 was calculated using an X-tile plot (version 3.6.1, Yale University) by dividing Ki67 data into two populations: low and high, with randomized 1:1 “training” and “validation” cohorts. Results: Median age was 51.5 years. 18.7% (n=15) presented with metastasis at the time of diagnosis and their overall median PFS was found to be 25.8 months. The incidence of HER2 positive LBBC was found to be 15% (n=12) and none of them were found to be presented with metastasis. Survival and frequency of various sub groups in our study are enlisted in the given table. We estimated a Ki67 cut-off of 30% in patients with upfront metastatic disease and PFS was found to be higher in <30% compared to a Ki67 index >30% (38.9 months vs 19.7 months, p-0.002). Overall median DFS was not achieved in non-metastatic group (Mean DFS: 64.7 months) where as a statistically significant difference was observed in the survival of HER2 positive (median DFS: 53.5 months, mean DFS: 50.9) than HER2 negative patients (median DFS not achieved, mean: 66.97 months) ( p-0.021). We obtained a Ki67 cut-off of 32% in non- metastatic group and mean DFS was found to be higher in Ki67<32% (69 months) compared to Ki67>32% (61.4 months), however it failed to exhibit a statistically significant relationship ( p-0.373). Conclusions: Our study indicates that a subset of patients exists within metastatic and non-metastatic LBBC with differing prognosis based on Ki67. Larger studies are further required to confirm the findings and therapeutic implications.[Table: see text]