Abstract

A case of apocrine adenocarcinoma arising in the scalp is reported. A 69-year-old male presented with an ulcerated nodular reddish firm mass in his scalp and two subcutaneous nodules in the left side of his neck. The biopsy suggested a metastatic adenocarcinoma, but a whole body CT, Ga scintigram and other examinations revealed no evidence of malignant tumor in other organs. Therefore we diagnosed it as sweat gland carcinoma and the wide resection and total neck dissection were done. The histopathology of the resected tumor showed adenocarcinoma with varying degrees of differentiation, composed of cords and nests which occasionally formed branching lumina. Atypical epithelial cells had abundant eosinophilic cytoplasm and only rarely showed projections from the apical cytoplasm consistent with decapitation secretion. Some tumor cells and luminal eosinophilic material were PAS positive, diastase-resistant, and were also alcian blue and CEA positive. By electron microscopy, the epithelial cells showed enlarge and rounded mitochondria and electron dense secretory granules, but no tonofilaments in the cytoplasm. Microvilli were seen along the luminal membrane. Infrequently apical membranes protruded in the lumen and showed typical dividing membrane. In addition, myoepithelial cells were seen along the basal epithelial membranes that led us to the final diagnosis of apocrine adenocar-cinoma.
It is difficult to make a diagnosis of carcinoma of sweat glands, especially in poorly differentiated cases, because of the histological similarity to metastatic adenocarcinoma in the skin. Apocrine adenocarcinoma that usually occurs in axilla or wherever apocrine glands normally exist and has high risk of regional lymph nodes metastasis is an uncommon neoplasm. Our case of apocrine adenocarcinoma of the scalp is the 4th reported case in Japan. Immuno-histochemical stainings are likely to be overused to make a diagnosis of sweat gland carcinoma. We should be reminded that some basic histological features such as decapitation secretion or myoepithelial cells which are elongated cells surrounding tumor nests and positive for smoothmuscle actin are still very contributory to define these tumors.
Mishima and Morioka suggest sweat gland tumors can be classified according to their anatomical origin and malignancy that provide us relatively clear-cut concept of these tumors. Using Mishima and Morioka system, we classify this tumor as an apocrine spirocarinoma because of the presence of decapitation secretion and myoepithelial cells, and the absence of tonofilaments.