Malignant breast adenomyoepithelioma with diagnostic discordance: a case report and literature review.

Malignant adenomyoepithelioma (MAME) of the breast is a rare biphasic neoplasm with potential for local recurrence and distant metastasis. Preoperative diagnosis is often difficult because core needle biopsy (CNB) may undersample the biphasic and malignant features of the tumor. We report an 84-year-old woman, among the oldest described patients, who presented with a newly palpable left breast nodule. Breast ultrasonography demonstrated an indistinct hypoechoic subareolar lesion, and mammography showed a corresponding focal asymmetry without suspicious calcifications. CNB suggested invasive carcinoma of no special type with a triple-negative immunophenotype. The patient underwent breast-conserving surgery (BCS) with sentinel lymph node biopsy (SLNB) and an intraoperative radiotherapy (IORT) boost. Final pathology confirmed grade 3 malignant MAME measuring 16 mm, with perineural invasion and a Ki-67 proliferation index of 20%. Immunohistochemistry confirmed a biphasic epithelial and myoepithelial nature. Surgical margins were negative, and sentinel lymph nodes were uninvolved. The patient subsequently received adjuvant capecitabine chemotherapy and supplemental whole-breast irradiation (WBI), with only grade 1 hand-foot syndrome, and showed no evidence of disease at 15 months of short-term follow-up. A pooled literature review showed substantial discordance between CNB and final pathology, supporting complete excision with comprehensive immunohistochemical evaluation. The principal contribution of this report is to highlight histologic-subtype discordance, in contrast to the malignancy-level discordance more commonly described, as a complementary diagnostic challenge in MAME. Across reported cases, negative-margin resection remained the cornerstone of management, lymph node involvement was uncommon, and late recurrence or distant metastasis could occur.