In patients with advanced breast cancer, most new calcifications detected on a mammogram after neoadjuvant chemotherapy are benign dystrophic calcifications, but this is not always observed. We present a patient with advanced breast cancer who had paradoxically increased malignant microcalcifications concomitant with primary tumor regression after undergoing neoadjuvant chemotherapy. After the neoadjuvant chemotherapy, the follow-up mammogram revealed that local, fine pleomorphic microcalcifications had markedly increased. Pathologically, these calcifications were ductal carcinoma in situ. We concluded that, in patients with breast cancer undergoing neoadjuvant chemotherapy, newly developed microcalcifications on follow-up mammograms should be carefully evaluated, and any suspicious malignant microcalcifications should be included in surgical excision planning.