Extrauterine adenosarcoma arising in omental endometriosis: rare site of occurrence of a rare tumor

Hidradenocarcinoma (HC) is an extremely rare malignant tumor originating from skin appendages, accounting for approximately 6% of malignant sweat gland tumors and less than 0.001% of all tumors. Sweat gland carcinoma with endocrine mucin-producing sweat gland carcinoma belongs to the category of low-grade cutaneous neuroendocrine carcinoma. Due to its extremely low incidence, lack of distinct clinical manifestations, and multiple pathological features, the clinicopathological diagnosis is challenging, often leading to misdiagnosis. To date, fewer than 20 cases have been reported in the literature. Low-grade cutaneous neuroendocrine carcinoma (LGNECS) has been proposed as a novel primary skin tumor with neuroendocrine differentiation. This study presents the clinicopathological characteristics of two cases of LGNECS and conducts a literature review. In case 1, the biopsy suggested squamous cell carcinoma (SCC), and in case 2, the biopsy indicated a tumor derived from skin appendages. However, postoperative histopathological examinations in both cases diagnosed low-grade sweat gland carcinoma with neuroendocrine differentiation. LGNECS poses significant challenges to clinicopathological diagnosis. Case 1: An 86-year-old male presented with a nodular lesion on the left temporal region, which had been present for one year. The lesion, measuring 3.5 × 2.5 cm, was ulcerated with partial crusting. Biopsy initially suggested SCC. However, the postoperative diagnosis was low-grade sweat gland carcinoma with neuroendocrine differentiation. Case 2: A 74-year-old female developed red papules on the lumbosacral region three years ago, each approximately 1 cm in size, accompanied by skin ulceration. The lesion was initially not considered significant. Over time, the mass increased in size and developed a foul odor. Biopsy suggested sweat gland carcinoma, and the postoperative diagnosis confirmed low-grade sweat gland carcinoma with neuroendocrine differentiation. Both patients received no treatment after surgery and have been followed up for 4 to 16 months, with no recurrence or metastasis observed. Sweat gland carcinoma with neuroendocrine differentiation is extremely rare, and biopsy is prone to misdiagnosis. A definitive diagnosis requires a comprehensive analysis of postoperative specimens combined with immunohistochemical studies. This study reports two cases of sweat gland carcinoma with neuroendocrine differentiation, providing valuable insights for clinicians and pathologists.