Atypical carcinoid tumor of the lung

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Abstract
Human atypical carcinoid tumors (17) of the lung that are histologically intermediate between small cell undifferentiated carcinoma and typical carcinoid tumor are described. Atypical carcinoid tumors have a distinctive microscopic pattern of nests, trabeculae and ribbons of intermediate-sized, moderately pleomorphic cells that lack the nuclear molding and dense hyperchromasia of small cell undifferentiated carcinoma. Mucin was present in 15 cases and 9 contained argyrophilic granules. The 3 primary tumors and 1 metastasis studied ultrastructurally contained dense-core granules and variable degrees of squamous and glandular differentiation. Eleven patients were men; 6 were women. Their mean age was 58 yr. Sixteen patients were known smokers. Twelve tumors involved the upper lobes and 3 were located in the right middle lobe. Mean tumor size was 4.9 cm (median 4; range 2.5-20). Four of 13 patients having potentially curative resection died of tumor. The other 9 patients were disease free with a mean follow-up of 20 mo. Four additional patients treated palliatively died.