Pathologic Complete Response After Neoadjuvant Chemotherapy in Breast Cancer Patients Treated With Mastectomy: Indications for Treatment and Oncological Outcomes.

Objective: The aim of this study was to evaluate the clinical outcomes of breast cancer (BC) patients treated with neoadjuvant chemotherapy (NAC) followed by mastectomy, focusing on cases achieving pathologic complete response (pCR). The implications of residual ductal carcinoma in situ (DCIS) on prognosis and survival were examined.

Materials and methods: A retrospective cohort study included BC patients treated with NAC followed by mastectomy at the breast unit of IRCCS Humanitas Research Hospital between March 2010 and October 2021. Patients were sub-grouped into two: Those with residual DCIS (ypTis) and those with complete response without residual tumor (ypT0). Key variables such as demographics, tumor characteristics, treatment regimens, and survival outcomes were analyzed.

Results: Of 681 patients treated with NAC, 175 achieved pCR, with 60 undergoing mastectomy. Among these 60 patients, 24 had residual DCIS (ypTis) while 36 had no residual invasive or in situ disease (ypT0). Patients with ypTis had higher rates of multifocal disease (62.5% vs. 27.8%, p = 0.006) and stage III disease (37.5% vs. 11.1%, p = 0.046). Triple-negative breast cancer was more prevalent in the ypT0 group (55.6% vs. 20.8%, p = 0.005). During a mean follow-up of 47 months, 11 patients experienced recurrence, with no significant differences in disease-free survival (DFS) and overall survival (OS) between the groups (p = 0.781, p = 0.963, respectively).

Conclusion: Residual DCIS after NAC did not significantly impact DFS or OS compared to complete pathologic response without residual DCIS. This study underscores the need for further research to refine pCR definitions and improve NAC's prognostic and therapeutic roles in BC management.