Clinical significance of residual microcalcifications after neoadjuvant chemotherapy: MRI response and the subtypes

The clinical significance of residual microcalcifications after neoadjuvant chemotherapy (NAC) in breast cancer remains unclear. We aimed to investigate whether residual malignant microcalcifications after NAC are associated with residual malignant disease in patients with breast cancer stratified by subtypes and MRI findings. We collected data retrospectively from January 2007 to December 2022. We evaluated the presence of suspicious microcalcifications on both pre- and post-NAC mammography. We defined a complete MRI response as the resolution of suspicious enhancement in the breast and axilla after NAC. We included 518 patients who had malignant microcalcifications before and after NAC, with 93/518 (18.0%) achieving a complete MRI response. In HR+ HER2-, 158/167 (95.2%) did not achieve pathological complete response (pCR) in breast, regardless of MRI response. Among the complete MRI responders, breast pCR rates were 87.2% (34/39) in HR- HER2+ breast cancer, and 91.7% (11 of 12) in TNBC, and 87.5% (14/16) in HR+ HER2+ breast cancer with limited extent of microcalcifications (<2 cm), respectively. Our findings suggest that despite persistent malignant microcalcifications after NAC, reducing surgical extent might be feasible among highly selected patients by MRI response.