What happened, in summary

A 51-year-old woman was evaluated after a newly detected left axillary mass measuring about 3.1 × 1.5 cm. She had no palpable mass in either breast, no nipple discharge, and no enlarged right axillary nodes. Ultrasound showed 3 irregular hypoechoic masses in the left axilla, and PET/CT showed increased glucose uptake in the same lymph-node area, while mammography and breast ultrasound did not identify a breast tumor. Fine-needle aspiration of a left axillary node showed invasive ductal carcinoma consistent with breast origin. Biomarker testing showed ER 90%, PR 80%, HER2 score 2+, Ki-67 70%, E-cadherin positivity, AR 90%, GATA3 positivity, and GCDFP-15 positivity; routine serum tumor markers, including AFP, CEA, CA19-9, and CA15-3, were within normal ranges. She had no disclosed personal or family history of malignancy. The working diagnosis was occult breast cancer, a presentation in which breast cancer is found through axillary nodal disease even though the primary breast lesion is not visible on initial imaging. She underwent left nipple-sparing mastectomy with axillary lymph node dissection. Surgical pathology found invasive carcinoma in the dissected axillary nodes and predominantly intermediate-grade ductal carcinoma in situ in the left breast. Repeat immunostaining remained ER-positive and PR-positive, with HER2 score 2+ and Ki-67 positivity. Adjuvant chemotherapy was part of her postoperative care after the breast and axillary surgery. At 1 year after surgery, she was recurrence-free. The case highlights the need to evaluate axillary disease carefully even when breast imaging appears negative. Post-surgical Ki-67 values were also documented at 25% and 40% in sampled tumor areas.