Molecular Subtypes As Emerging Predictors of Clinicopathological Response to Neoadjuvant Chemotherapy (NACT) in Locally Advanced Breast Cancer (LABC): A Single-Centre Experience in Western India

Introduction: Locally advanced breast cancer (LABC) is a subset of breast cancer characterized by the most advanced breast tumours in the absence of distant metastasis. Treatment of LABC has evolved from a single modality treatment to multimodality management. Neoadjuvant chemotherapy (NACT) is increasingly being used to treat patients with LABC. This study assessed tumour response after NACT using clinical changes, Response Evaluation Criteria in Solid Tumors (RECIST) criteria and pathological report. Methodology: This study was a prospective as well as retrospective observational study carried out in the department of general surgery, Dr. Sampurnanand Medical College, Jodhpur. All the patients admitted with stage III (IIIA, IIIB, IIIC) were included in the study after obtaining approval from the institutional ethical committee. Clinical response was assessed by RECIST criteria (clinical complete response (cCR), clinical partial response (cPR), clinical progressive disease (cPD), and clinical stable disease (cSD)) and pathological response by histopathological report (pCR). Response of various molecular subtypes was noted. Results: Among 31 patients included in the study, cCR observed in 22.58% cases, cPR observed in 61.29% cases while cPD and cSD seen in 3.22% and 12.90% cases, respectively. Pathological complete response (pCR) observed in 19.35% cases. Favourable response seen with human epidermal growth factor receptor 2 (HER2) overexpression (cCR = 50%, pCR = 37.50%) followed by triple negative (cCR = 25%, pCR = 25%) molecular subtypes. Conclusions: It can be concluded that molecular subtype determination helps in deciding treatment protocol in patients with LABC with HER2 overexpression and triple-negative breast cancers having a better clinicopathological response to NACT than luminal subtypes. NACT results in downstaging of tumours, thus, help in achieving surgically clear margins and elimination of micrometastases which decreases the recurrence rates and morbidity/mortality of patients.