A Case of HER2-Positive Paget's Disease with Extensive Ductal Carcinoma in Situ

Abstract

The patient was a 63-year-old woman. An erythematous erosion on her left breast had appeared 7 years earlier and gradually enlarged. On examination at our hospital, a 7.5 × 5.5 cm oval, reddish, eczematous lesion centered on her left nipple was noted. It was diagnosed as Paget's disease by skin biopsy. Magnetic resonance imaging showed a non-mass-like enhancement with a diameter of approximately 5 cm in the breast, and it was assumed that ductal carcinoma in situ (DCIS) had spread within this area. Mastectomy and sentinel lymph node biopsy were performed, and the histopathological diagnosis was Paget's disease, n0, no invasion, ER-negative, PgR-negative, HER2 score 3+. High-grade DCIS was found in the breast, and its range was 9.0 cm, which was larger than on the preoperative diagnostic imaging. Preoperative diagnosis of the spread of intramammary lesions is of paramount importance in the surgical treatment of Paget's disease of the breast, as in other breast cancers. The lesion should be resected reliably, without underestimating the extent of DCIS.