PATTERN OF HER-2 EXPRESSION WITH SPECIAL REFERENCE TO LOW HER-2 EXPRESSION IN IHC SAMPLES OF BREAST CANCER PATIENTS AT TERTIARY CANCER HOSPITAL HCG AHMEDABAD

Background: Breast cancer is the 2nd most common cancer worldwide and number one cancer in women. As per American Society of Clinical Oncology 2018 guidelines, HER2 classification is binary HER2 positive and HER2 negative. DESTINY-Breast04 trial (2022), the FDA expanded the approval of the HER2 antibody-drug conjugate (T-Dxd) from metastatic breast cancer patients with HER2 protein over-expression/amplification, to also include metastatic patients with HER2 IHC 1+ or 2+ & ISH negative results. This clinical trial adopted a new terminology, HER2 Low, which successfully prolonged both progression-free survival (PFS) and overall survival (OS). Material and Method: A descriptive and retrospective analysis was performed, including all patients diagnosed with Invasive breast cancer in HCG cancer Centre, Ahmedabad- Triesta Laboratory between 1st July 2022 to 31st June 2023. Total of 395 patients of both genders were studied. All those individuals who were diagnosed with Invasive breast carcinoma according to WHO and CAP guideline by H&E, IHC and FISH test were included in our study and those with missing data were excluded from our study. Result: This was a descriptive and retrospective study where 395 cases were diagnosed as breast cancer. HER2 low pattern was found commonly in 4th and 6th decades of life. In our study, out of 395 cases, 34.9% (n = 138) were HER2-negative, 39.5% (n = 156) were HER2-low, and 25.6% (n = 101) were HER2-positive. Among 156 HER2-low cases, 15.4% (24/156) cases were hormone negative, and 84.6% (132/156) cases were hormone positive. Conclusion: We observed that approximately 40 % of the cases were recategorized to be HER2 low which were classified HER2 negative according to old guidelines. Approximately 84% cases of HER2 low group were hormone positive. With the development of novel ADCs and other targeted agents, the treatment strategies for HER2-low breast cancer are expanding, and hence detecting low expression levels of HER2 is important.