Prevalence of low HER2 expression in breast cancer patients: An Indian experience.

Abstract

e12543 Background: With the recent advent of trastuzumab deruxtecan and encouraging results of the DESTINY-Breast-04 trial, low HER2 expression has emerged as a clinically significant therapeutic biomarker. The prevalence of low HER2 expression is unexplored in Indian population. Methods: This is a single center ambispective observational study conducted over a period of 4 years (1st January 2019 to 31st January 2023) at Dr. B.R.A, I.R.C.H, All India Institute of Medical Sciences (AIIMS), New Delhi, India. Consecutive female breast cancer patients registered during the study period with available clinical-pathological details were eligible for study inclusion. The primary objective of the study was to assess the prevalence of HER2 low breast cancer. HER2 low was defined as having HER expression by immunohistochemistry (IHC) of 1+ or 2+ with no amplification of the HER2gene detected with a fluorescent in situ hybridization (FISH) assay. Patients were divided into three categories: HER-2 high (IHC3+, IHC2+/FISH+), HER-2 low (IHC 1+, IHC2+/FISH-), and HER2-0 (HER2 negative, IHC:0). Staging description of the cases were done as per anatomic TNM classification according to AJCC 7th edition. Results: A total of 2200 female breast cancer were registered during the study period, of which 1932 patients had available clinical-pathological details. Among 1932 patients, 600 patients (31%) had high HER2 expression and remaining 1332 patients had HER2 low/HER2-0 expression. Of the 1332 cases, the median age was 49 years (range 18–91 years). The stage distribution was stage I, 94 (7.06%); stage II, 409 (30.70%); stage III, 528 (39.64%); and stage IV, 301 (22.59%). Eight hundred patients (60.06%) were hormone positive, and 532 (39.94%) cases were hormone negative. The prevalence of HER2 low expression was 798 (59.9%). It was observed in 640 (80%) of hormone positive cases and 158 (29.69%) hormone-negative cases (p < 0.001). Rest 534 cases were HER2 0 [160 cases (20%) were hormone positive, and 374 cases (70.31%) were hormone negative]. Conclusions: This is the first study from India to document the prevalence of low HER2 expression in female breast cancers. We observed the prevalence to be around 60 % in our population, which is more in hormone receptor-positive breast cancer. The estimated prevalence is higher than that observed in Western population, and it underscores the need to systematically categorize these patients for therapeutic decision making at presentation.