What happened, in summary

This 55-year-old woman was evaluated after screening found abnormalities in the left breast. She was menopausal and had no personal or family history of breast cancer. Examination found a nonfixed palpable mass in the left lower central breast. Mammography showed a 3 cm irregular hyperdense mass without microcalcifications, and ultrasound showed an irregular hypoechoic solid mass. Chest CT showed the left breast mass but no enlarged axillary lymph nodes. Breast MRI showed rim enhancement and a washout curve, while diffusion imaging showed a low tumor ADC value and a high peritumoral-to-tumoral ADC ratio. She underwent partial mastectomy with sentinel lymph node biopsy. The tumor measured 3.1 cm and showed lymphatic invasion, but sentinel and axillary lymph nodes did not contain metastases. Microscopy showed large polygonal tumor cells with abundant cytoplasm arranged in solid nests, cellular pleomorphism, occasional nucleoli, and many mitoses. Immunohistochemistry showed diffuse HER2 staining and positivity for neuroendocrine markers INSM1 and synaptophysin. The tumor cells were negative for estrogen receptor, progesterone receptor, chromogranin, and neuron-specific enolase. This profile supported breast carcinoma with neuroendocrine differentiation rather than ordinary hormone receptor-positive breast cancer. The surgical resection was completed without perioperative complications. No recurrence or metastasis was seen before she was lost to follow-up, so the long-term outcome cannot be confirmed beyond the available postoperative period. Because no additional clinic visits occurred after the early postoperative period, her course is best described as completed local treatment with limited follow-up. The important supported cancer details are the HER2-positive, ER/PR-negative profile and neuroendocrine-marker expression.