What happened, in summary

A 49-year-old premenopausal woman noticed a right breast lump that had been present for two weeks. Examination found a hard 40 mm mass without nipple, skin, or discharge changes. She underwent total mastectomy with sentinel lymph-node biopsy. The surgical specimen contained two tumors measuring 55 mm and 10 mm. Both were ER-negative, lacked HER2 overexpression, and had a Ki-67 index of 90%. Microscopy showed small malignant cells, necrosis, and high mitotic activity. Neuroendocrine markers including synaptophysin and chromogranin A were positive, and the overall findings supported primary small-cell neuroendocrine carcinoma of the breast. Two sentinel nodes were free of metastasis. Her postoperative recovery was uncomplicated. A multidisciplinary team concluded that the breast tumor had been radically removed and recommended adjuvant chemotherapy followed by postoperative radiation. She was referred for oncology treatment. Because this rare tumor can resemble small-cell cancer metastatic from another organ, the diagnosis depended on combining pathology with evaluation for another primary site.