The effect of neoadjuvant chemotherapy on ductal carcinoma in situ in triple-negative breast cancer patients: A nationwide analysis.

Purpose: Recent studies show that ductal carcinoma in situ (DCIS) accompanying HER2+ breast cancer can be completely eradicated following neoadjuvant systemic therapy in up to 52 %. We aimed to determine the complete response rate of DCIS in triple-negative breast cancer (TNBC) patients in a nationwide cohort and to assess clinicopathological variables associated with response. Furthermore, the impact on surgical treatment after neoadjuvant chemotherapy (NACT) was investigated.

Methods: Women diagnosed with TNBC, treated with NACT followed by surgery, between 2010 and 2020, were selected from the Netherlands Cancer Registry (NCR). Pre-NACT and postoperative pathology reports were obtained from Palga, the Dutch nationwide pathology databank, to determine presence of DCIS. Clinicopathological factors associated with DCIS response were investigated using uni- and multivariable logistic regression analysis.

Results: In total, 4494 patients were included. A DCIS component was present in the pre-NACT biopsy of 442 (9.8 %) patients. Pathologic complete response of the DCIS component was achieved in 53.6 % of these patients. The presence of calcifications in the pre-NACT biopsy was associated with a lower chance of DCIS response in univariable logistic regression analysis (OR 0.52, CI 95 % 0.27-0.98, p = 0.04). In multivariable analysis, no statistically significant associations were found between DCIS response and clinicopathological variables. Mastectomy rates were higher in case of IBC + DCIS compared to IBC (53.4 % vs 40.1 %, p < 0.001).

Conclusion: Pathologic complete response of DCIS to NACT occurred in 53.6 % of TNBC patients. Future studies are required to be able to predict DCIS response based on clinicopathological variables and imaging.