Primary small-cell carcinoma of the breast: a case report.

We report a case of small-cell carcinoma of the breast. The patient was a 54-year-old Japanese woman with a left breast mass. Mammography revealed a 1.2-cm microlobulated mass with partially ill-defined borders. Ultrasonography disclosed a hypoechoic mass measuring 1.8 × 1.2 × 1.2 cm with heterogeneous internal echoes and partially ill-defined borders. The shape of the mass was round and taller than it was wide in the orthogonal section to the longest axis of the mass. These imaging findings suggested a malignant tumor. Fine-needle aspiration cytology of the tumor also suggested a ductal carcinoma. Breast-conserving surgery was performed with axillary sentinel lymph node biopsy. A diagnosis of small-cell carcinoma of the breast was made based on the histologic and immunohistochemical findings. This rare breast tumor has been reported to be aggressive and associated with a poor prognosis; however, our patient is currently well and has had no clinical recurrence of the disease after 5 years of follow-up without radiotherapy or chemotherapy. Therefore, the prognosis may be better if the tumor is detected early and there is an absence of lymph node metastasis.