The impact of pathological complete response on survival in patients with breast cancer and occurrence in different intrinsic subtypes: A retrospective observational study

Background: Pathological complete response (pCR), defined as non-invasive or in situ disease in the breast and regional lymph nodes following neoadjuvant chemotherapy (NACT) predicts oncologic outcomes. Objectives: The primary objective was to study the impact of pCR on survival in patients with breast cancer. The secondary objective was to assess the pCR rates in various intrinsic subtypes of breast cancer. Materials and Methods: This was a retrospective observational study conducted between 2015 and 2020 in the Department of Radiotherapy at R.G. Kar Medical College and Hospital, a tertiary care institution in Kolkata in eastern India, in women with locally advanced breast cancer (LABC) who received NACT. Patients were categorized based on age, menopausal status, and tumor characteristics, including stage, grade, and immunohistochemistry (IHC). The pCR rate was assessed, along with the median disease-free survival (DFS) and overall survival (OS). Results: A total of 251 patients (median age, 50 years; interquartile range, 43–57) were enrolled; 42 (16.7%) attained a pCR. Among the patients who attained a pCR, 7 (16.7%) had Luminal A, 8 (19.0%) had Luminal B, 14 (33.3%) had triple-negative breast cancer (TNBC), and 13 (31%) had HER2-positive disease. The median DFS for the entire cohort was 65 months (95% CI, 59.7–70.3); the median OS was not reached. The 5-year DFS in patients who attained a pCR was 67% compared to 52% in those who did not; P = 0.04. The 5-year OS was 92% and 74% in patients who attained a pCR and those who did not, respectively; P = 0.024. Conclusion: Patients with LABC who attain a pCR following NACT have better survival, both DFS and OS, compared to those who do not. The implications of this are particularly relevant in patients with HER2 enriched and triple negative breast cancer and are crucial in guiding the intensification of therapy in the adjuvant setting.