A case of sweat-gland carcinoma with neuroendocrine differentiation.

Abstract

Low-grade neuroendocrine tumors, also known as carcinoid tumors, are slow-growing cancers derived from neuroendocrine cells, usually found in the digestive tract or lung lining; the primary tumor in the skin is extremely rare and is called sweat-gland carcinoma with neuroendocrine differentiation (SCAND) as a new disease concept.1-4 Herein, we report a case of SCAND on the lower abdomen presenting bilateral inguinal lymph node metastasis. A 73-year-old Japanese male patient presented to our hospital with a 5-year history of a red nodule arising from the lower abdomen to the base of the penis. He has a medical history of hypertension, atrial fibrillation, and cerebral infarction. Physical examination revealed a red mulberryshaped nodule with red papules (Figure 1A) and enlarged, elastic, and complex lymph nodes at the bilateral inguinal region. Dermoscopy showed branched and/or partially reticular vessels on a pale red structureless area (Figure 1B). Contrastenhanced computed tomography revealed two tumors in the left kidney. They were renal cell carcinomas classified as cT1aN0M0 stage I with a low probability of metastasis, and no other visceral malignancies were found. 18F-fluorodeoxyglucose positron emission tomography integrated with computed tomography showed abnormally increased cellular uptake of glucose on the lower abdomen and bilateral inguinal lymph nodes; however, the left renal tumors and other sites showed normal uptake. Skin biopsy revealed various-sized tumor nests diffusely infiltrated from dermis to subcutaneous tissue (Figure 2A-B). Focal pagetoid extension of the tumor cells within the overlying epidermis was observed. The tumor cells were small to medium size, with abundant and pale eosinophilic cytoplasm, round-to-oval nuclei, and coarse granular chromatin pattern. Few nuclear atypia and mitotic figures were observed (Figure 2C). A tumor mass floating in abundant mucus was observed in part of the tumor (<10%) (Figure 2D). Alcian blue staining (pH 2.5) showed extracellular mucin deposition. The metastatic lymph nodes were almost replaced by tumor cells that showed a trabecular growth pattern (Figure 2E). Immunohistochemical staining of the tumor cells was positive for cytokeratin 7, estrogen receptor, progesterone receptor, chromogranin A, synaptophysin, CD56, and GATA3 and negative for cytokeratin 20. Consequently, we diagnosed this tumor as SCAND. However, the scheduled surgery was canceled due to multiple cerebral infarctions. SCAND was a newly proposed entity and sporadic disease in 2022. It commonly occurs on milk-lines on the trunk of middle-aged to elderly males and often causes lymph node metastasis.4 In our case, histopathologically, a tumor mass floating in a large amount of mucus was observed in part, and primary cutaneous mucinous carcinoma (PCMC) with neuroendocrine differentiation was the differential diagnosis. However, since this feature accounts for only a tiny fraction of tumors (<10%) and PCMC occurs primarily in the head and neck region, we thought PCMC could be ruled out. Consequently, while SCAND and PCMC sometimes share histologic similarities, their differentiation is important because PCMC rarely metastasizes while SCAND often does.5 It has not been long since the SCAND concept was proposed, and more cases are expected to accumulate.