Low-Grade Adenosquamous Carcinoma of the Breast: A Case Report.

Introduction: Low-grade adenosquamous carcinoma (LGASC) is categorized as a metaplastic carcinoma but differs from other types of metaplastic carcinoma in having a more favorable prognosis. Due to its rarity and unusual and inconsistent presentation, there is little information available regarding its characteristics, making correct diagnosis a challenge.

Case presentation: We report herein the case of a 54-year-old Japanese woman who presented with a lump in her left breast. She was found to have a benign lesion which continually relapsed, necessitating repeated excisions, ultimately leading to the diagnosis of LGASC after the third excision. Guidelines for the treatment of LGASC emphasize complete tumor excision, with adjuvant therapies only considered in cases with positive lymph node metastasis. Consequently, the patient underwent total mastectomy but postoperative chemotherapy was not administered, and the patient was followed up with regular observation. By 20 months postoperatively, there was no sign of recurrence.

Conclusion: LGASC has distinctive pathological features of the intimate admixture of well-developed glands and solid squamous cell nests within a fibrotic or cellular spindle stroma. It is difficult to determine preoperatively with cytology or needle biopsy because LGASC mimics benign tumors. It is typically triple-negative, but it has an indolent behavior. Adjuvant therapy after surgery is considered unnecessary for triple-negative status, but there is no clear evidence. We aimed to provide more data on the disease characteristics, presentation, and treatment outcome. Accumulation of further evidence is warranted to refine diagnostic and therapeutic strategies of LGASC.