High-grade adenosquamous carcinoma (HGASC) is a rare and aggressive subtype of metaplastic breast cancer (MpBC). This article reports a case of HGASC (pT2N0M0 Stage IIA) in a 43-year-old female and reviews the relevant literature, with a specific focus on distinguishing HGASC from other MpBC subtypes, particularly low-grade adenosquamous carcinoma (LGASC). The patient underwent a skin-sparing mastectomy with abdominal rectus myocutaneous flap reconstruction. Histopathology confirmed HGASC with metaplastic features. Postoperative adjuvant chemotherapy with capecitabine was administered. The case highlights the unique clinical, imaging, and pathological characteristics of HGASC, its therapeutic challenges, and the need for individualized treatment strategies. A five-month follow-up showed no signs of recurrence or metastasis.