A Prospective Multi-Institutional Observational Study on ER, PR, HER2/NEU, and Ki-67 Expression and Discordance Pattern in Primary and Metastatic and Recurrent Carcinoma Breast and Its Therapeutic Implications and Prognostic Outcome

Only few studies reported in literature that has elucidated in detail the implications of molecular typing in metastatic and recurrent breast cancer. In this prospective study, we have analysed in depth the pattern of expression, discordances of molecular markers in various metastatic sites, and recurrent cases and their response to chemotherapy/targeted agents and the prognostic outcome. The primary aim of the study was to determine ER, PR, HER2/NEU, and Ki-67 from recurrent and metastatic carcinoma breast to study the expression pattern and discordance and also to study the degree of discordance in relation to the site of metastasis and pattern of metastasis (synchronous vs metachronous) and discordance pattern with the response to chemotherapy and median overall survival rates in months in available subset of patients. Prospective open-label study done at the Government Rajaji Hospital, Madurai Medical College, and Government Royapettah Hospital, Kilpauk Medical College, India, from November 2014 to August 2021. All breast carcinoma patients with recurrence or oligo metastasis (defined as one organ with less than 5 metastases in our study) with known receptor status were eligible and 110 patients were enrolled in the study. ER (ER + to ER -) discordance was seen in 19 (26.38%) cases. PR (PR + to PR -Ve) discordance was seen in 14 (19.17%) cases. HER2/NEU (HER2/NEU + Ve to -Ve) discordance was seen in 3 (16.6%) cases. Ki-67 discordance was seen in 54 (49.09%) cases. High Ki-67 as a proliferative marker has increased response to chemotherapy but earlier relapse and disease progression especially in Luminal B type. In further subset analysis, ER, PR, and HER2/NEU discordance is higher for lung metastasis (ER, PR 61.1%, p value .001, HER2/NEU 5.5%), followed by liver metastasis (ER, PR 50%, p value .0023, 1 case turning ER -ve to + ve, HER2/NEU 1 (10%)). In lung, discordance is more for metachronous metastasis. In liver, discordance is 100% for synchronous metastasis. Synchronous metastasis with discordance in ER and PR is associated with rapid disease progression. High Ki-67 subset of Luminal B-like tumors progressed rapidly than triple negative and HER2/NEU positive subset. Complete clinical response rate in contralateral axillary node metastasis group was 87.8%, followed by local only recurrence with high Ki-67 where chemotherapy had response rate of 81% and 2 years DFS of 93.12% after excision. Certain subsets like contralateral axillary nodes and supraclavicular nodes which present as oligo metastatic disease with discordance and high Ki-67 respond well to chemotherapeutics and targeted agents improving the OS in this subset of patients. Molecular markers and their expression and discordance pattern determine the therapeutic outcome and prognosis of the disease. Early identification and targeting the discordance would go a long way in improving the outcome and DFS and OS of breast cancer patients.