Extensive Axillary Nodal Metastasis Despite a Clinically Negative Axilla in Invasive Lobular Carcinoma: A Case Report.

Invasive lobular carcinoma (ILC) is a distinct subtype of breast cancer characterized by an infiltrative growth pattern that frequently limits the accuracy of clinical examination and conventional imaging. Although most ILCs are hormone receptor-positive and are often associated with favorable prognostic expectations, accurate diagnosis and staging require careful integration of imaging findings, histopathologic assessment, and definitive surgical evaluation. We present the case of a 50-year-old premenopausal woman who presented with a progressively enlarging right breast mass of more than two months' duration. Clinical examination revealed a firm breast lesion with skin tethering and no palpable axillary lymphadenopathy. Imaging demonstrated an irregular non-mass lesion in the right breast, and biopsy confirmed ILC with strong estrogen and progesterone receptor positivity, HER2 negativity, low proliferative index, and loss of E-cadherin expression. Despite favorable tumor biology and a clinically negative axilla, intraoperative sentinel lymph node biopsy using dual tracer mapping with methylene blue dye and technetium-99m radiotracer identified metastatic involvement, prompting completion axillary lymph node dissection. Final pathology revealed eight positive lymph nodes with extranodal extension, corresponding to pT2 pN2a disease. The patient underwent right skin-sparing mastectomy with immediate reconstruction, followed by multidisciplinary planning for adjuvant systemic therapy, radiotherapy, and long-term endocrine therapy. This case highlights that hormone receptor-positive ILC may still harbor significant regional nodal disease, underscoring the importance of comprehensive staging and multidisciplinary management.