Abstract PO3-06-03: Overall Survival and Disease Interval Among Breast Cancer Subtypes in Patients with Brain Metastasis
Authors: Shrestha Asis , Gouli Sugam , Niraula Sujan , Babbra Ramandeep , Neupane Niraj , Stanford Sarah , Strawderman Myla , Kharel Zeni , Zhang Huina , Hardy Sara , Mohile Nimish , Anders Carey , Hicks David , O'Regan Ruth , Dhakal Ajay 
Published: May 2024

Abstract
Background:
Breast cancer brain metastasis (bcbm) is associated with limited survival. There is a paucity of clinical trials and real-world data on the survival and disease interval [primary breast cancer (pbc) to metastatic breast cancer (mbc) or bcbm] of bcbm patients. We performed a retrospective study comparing the overall survival (OS) and disease intervals (INT) between the date of pbc surgery, diagnoses of mbc, and bcbm among 3 subtypes of bc in patients with bcbm.
Methods:
The informatics team generated a preliminary list of patients with a history of breast cancer and brain metastasis who were treated at the Wilmot Cancer Institute (WCI) of the University of Rochester. Key inclusion criteria were evidence of bcbm, bcbm diagnosed between Jan 1st, 2010 and June 1st, 2021, and adequate medical records available. Patients with de novo mbc were excluded. Final eligible patients were registered for the study. Median OS in bc subtypes was assessed with the Kaplan-Meier method and compared using the log-rank test. Median INTs among bc subtypes were compared using the Kruskal-Wallis test. Registered patients were divided into triple-negative (TNBC), estrogen receptor-positive/HER2 negative (ER+/HER2-), and HER2+ subtypes.
Results:
Out of 191 patients screened, 83 patients were eligible for the study. The total number of patients enrolled by subtype was 26 (TNBC), 35 (ER+/HER2-), and 22 (HER2+). Disease and patient characteristics are shown in Table 1. Median OS from pbc, mbc, and bcbm among 3 subtypes are shown in Table 2. The differences in the median OS from these 3 different time points were not statistically significant among 3 subtypes. After adjusting for important variables (age, race, tumor grade, stage, and presence of perioperative therapy) in a Cox regression model, there was still no statistical evidence that these 3 subtypes differed in OS. Three different INTs (pbc-mbc, pbc-bcbm, mbc-bcbm) among 3 subtypes are shown in Table 3. INTpbc-mbc and INTpbc-bcbm were significantly different among 3 subtypes of bc. After adjusting for the factors in the model, the subtypes didn’t differ significantly with respect to INTpbc-mbc and INTpbc-bcbm. Stage 3 at pbc was significantly associated with shorter INTpbc-mbc and INTpbc-bcbm. The distribution of INTmbc-bcbm was highly non-normal due to the high % of patients with concurrent diagnoses of mbc and bcbm. Thus an exploratory logistic regression model assessed the association of subtypes and important variables with the odds of having mbc and bcbm concurrently (INTmbc-bcbm&lt; 1 month). It showed that the ER+/HER2- subtype had 4 times lower odds of concurrent mbc and bcbm diagnosis than the HER2+ subtype (p=0.03). In an unadjusted pairwise comparison between the subtypes (Table 3), the ER+/HER2- group had statistically longer INTpbc-mbc and INTpbc-bcbm than TNBC. However, when the subtypes were adjusted for Stage 3 vs 1 or 2, these subtypes were not significantly different for these INT. In our study, a higher proportion of Stage 3 tumors in TNBC subtype is likely associated with the shorter INTs seen with TNBC in unadjusted analysis.
Conclusion:
Adjusted comparison of OS and disease intervals from pbc between TNBC, ER+/HER2-, and HER2+ subtypes were not statistically different in this cohort of bcbm patients. Interestingly, median OS from mbc were numerically very similar (3.6-3.7 years) among these subtypes. Median OS from pbc and bcbm were numerically longer in HER2+ bc than the other 2 subtypes. Intervals between pbc to mbc and to bcbm and between mbc to bcbm were numerically longer in ER+/HER2- subtypes than the other 2 subtypes. ER+/HER2- subtype was 4 times less likely to have concurrent bcbm at the time of mbc diagnosis than the HER2+ subtype. These results are exploratory and hypotheses generating.
Table 1: Disease and Patients Characteristics
Table 2: Overall Survival Unadjusted
Table 3: Disease Intervals Unadjusted
Citation Format: Asis Shrestha, Sugam Gouli, Sujan Niraula, Ramandeep Babbra, Niraj Neupane, Sarah Stanford, Myla Strawderman, Zeni Kharel, Huina Zhang, Sara Hardy, Nimish Mohile, Carey Anders, David Hicks, Ruth O'Regan, Ajay Dhakal. Overall Survival and Disease Interval Among Breast Cancer Subtypes in Patients with Brain Metastasis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-06-03.