Surgical treatment after neoadjuvant systemic therapy for HER2-positive invasive breast cancer in the Netherlands: 10-Year trends and the influence an accompanying DCIS component

Background: The presence of a DCIS component accompanying invasive breast cancer (IBC) is associated with a higher rate of primary mastectomy compared to IBC without DCIS. After neoadjuvant systemic therapy (NST), HER2+ IBC patients show high response rates, allowing for increasing breast-conserving surgery rates. The aim of this study was to examine surgical trends after NST in a Dutch nationwide HER2+ cohort, and the influence of a DCIS component on mastectomy rate. Methods: Women with HER2+ IBC, diagnosed between 2010 and 2019 and treated with NST and surgery were included from the Netherlands Cancer Registry. Mastectomy rate was examined over the years, and compared between patients with and without a DCIS component in the pre-NST biopsy. Multivariable logistic regression analysis was used to investigate the association of the DCIS component with mastectomy rate and likelihood of achieving ypT0. Results: In total, 5289 patients were included. Over 10 years, mastectomy rate significantly decreased from 62.6 % in 2010 to 35.1 % in 2019. Patients with IBC+DCIS more often underwent mastectomy, with a rate of 48.4 % in 2019, compared to 30.0 % in IBC only (p < 0.001). Percentage of ypT0 was significantly lower in patients with IBC+DCIS (38.7 %), compared to IBC only (47.3 %, p < 0.001) Multivariable logistic regression analyses showed presence of DCIS (OR 1.69, 95%CI 1.47–1.95, p < 0.001) to be independently associated with mastectomy. Conclusion: Rate of mastectomy decreased significantly in HER2+ IBC treated with NST between 2010 and 2019. Presence of DCIS in the biopsy remained associated with higher mastectomy rate, yet 38.7 % of these patients do achieve ypT0.