What happened, in summary

A 40-year-old woman presented with a palpable left axillary mass that had been present for 2 months. On examination, the mass was fixed and about 30 mm, with no redness, ulceration, or swelling of the overlying skin. She also had nipple induration in both breasts but no palpable breast mass. Ultrasound found benign cysts and fibroadenomas in the breasts, plus a solid spindle-shaped left axillary mass about 31 mm. MRI showed a well-defined 24 x 35 mm mass near the axillary nerve, so the initial differential included a nerve tumor such as schwannoma or a metastatic lymph node. Needle biopsy showed a spindle cell tumor with mild to moderate atypia. Excisional biopsy confirmed a malignant high-grade spindle cell neoplasm inside a lymph node, favoring metastatic disease. Immunostaining supported a triple-negative tumor: ER-negative, PR-negative, and HER2-negative. The tumor was CK-positive, S100-positive, focally vimentin-positive, and had a low Ki-67 index under 10%. PET-CT showed FDG uptake in the upper inner quadrant of the left breast and no pathologic uptake elsewhere, meaning no distant metastases were identified. She was diagnosed with triple-negative metaplastic breast cancer, spindle cell carcinoma subtype, with axillary lymph-node involvement. A formal stage was not stated. She received doxorubicin and cyclophosphamide for 6 cycles. Nipple induration improved mildly, and she then underwent left modified radical mastectomy with axillary lymph node dissection. Pathology showed a total burn-out tumor with no residual tumor cells in the breast, and all 19 dissected lymph nodes were free of tumor. At 1-year follow-up, she had no signs of recurrence.