When Hard Doesn't Mean Malignant: A Benign Axillary Finding in Lobular Carcinoma.

A 50-year-old premenopausal woman presented with an abnormal screening mammogram, which led to the diagnosis of grade 2 invasive lobular carcinoma of the left breast with axillary lymph node metastases. Immunohistochemistry confirmed lobular origin with estrogen receptor (ER)/progesterone receptor (PR) positivity and Human Epidermal Growth Factor Receptor 2 (HER2) negativity. Neoadjuvant chemotherapy with cyclophosphamide and docetaxel was followed by a sentinel lymph node biopsy, which revealed three metastatic nodes. A modified radical mastectomy with axillary dissection was subsequently performed. Postoperative pathology showed residual invasive lobular carcinoma measuring 1.7 cm, with negative surgical margins and angiolymphatic invasion. Notably, a hard axillary mass excised during dissection revealed a rare benign chondroid and osseous metaplastic reaction. This histologic finding, although non-malignant, may be confused with nodal disease intraoperatively or on imaging, underscoring the importance of thorough pathologic analysis. The patient completed post-mastectomy radiation therapy to the chest wall and regional lymphatics and was started on ovarian suppression and endocrine therapy with a Cyclin-dependent Kinase (CDK)4/6 inhibitor. Genetic testing was negative, and there was no family history of breast or ovarian cancer. This case draws attention to an uncommon histopathological response that may follow trauma or biopsy in breast cancer patients and reinforces the need for clinical awareness when interpreting persistent axillary findings post-treatment.