汗腺瘤(eccrine hidradenoma)是一種不常見的皮膚腫瘤，是由汗腺的遠端排泄管細胞發展而來。汗腺瘤多是良性、獨立的囊腫性腫瘤，通常在頭皮和腋窩。在此，我們報告一個乳房巨大的汗腺瘤，臨床表現疑似乳癌。這位52歲的女性在左乳與前胸廓有一顆緩慢長大的腫塊，已長達30年之久。理學檢查發現該腫瘤大小有21×17×10公分。在超音波檢查中，它是一個複雜的多囊性腫瘤，具有大量的低迴音液體成分和部分高迴音的固體病灶。電腦斷層掃描顯示腫瘤具有完整的邊界、多囊性且密度分布均勻的液體、和部分固體成分。臨床上懷疑是黏液型乳癌，建議病人接受了廣泛的腫瘤切除。在組織學檢查和免疫化學染色的判斷後，診斷為汗腺瘤。乳房是汗腺瘤的罕見部位，乳癌應該是主要的鑑別診斷。組織學確診是必要的，細針抽吸或許無法確診，此例以廣泛切除才適用於治療和診斷。

Eccrine hidradenoma (EH) is an unusual cutaneous neoplasm, believed to arise from the distal excretory duct of the eccrine sweat glands. Most EHs are benign and solitary cystic tumors usually on the scalp and axillae. Here, we report a huge EH exceptionally arising from the breast and clinically mimicking a breast cancer. The 52-year-old woman presented with an enlarging mass at her left breast for 30 years. The physical examination revealed a 21×17×10cm cystic mass. On ultrasound examination, it was a complex multilocular cystic lesion with massive hypoechoic fluid content. The computerized tomography scan demonstrated a well-circumscribed cystic mass with homogeneous water density, and foci of solid components. Under the impression of mucinous carcinoma, a wide excision was performed. Based on the histology and immunohistochemistry, the diagnosis of EH was made. While the breast is an uncommon site for EH, breast cancers should be the major differential diagnoses before excision. A histopathological confirmation is essential, and the wide excision is appropriate for both treatment and diagnosis.