Atypical carcinoid of the lung. A distinct clinicopathologic entity.

Eleven cases of atypical carcinoid (AC) of the lung were identified during an eight-year period. Their clinical features and treatment responses were contrasted with our experience at Vanderbilt with small cell lung cancer (SCLC) and a literature review of typical bronchial carcinoids (TC). Clinically, there were no features to distinguish AC from TC except for age at diagnosis (59 vs 49 years). Atypical carcinoid was similar to SCLC with respect to many clinical features, although female sex, absence of smoking history and localized disease at presentation were more common in AC. Pathologically, these tumors were distinguished by cellular atypia, necrosis, architectural disorder, or increased mitotic rate in the presence of a recognizable carcinoid pattern. Immunoperoxidase staining revealed no difference between AC and TC or SCLC. Atypical carcinoid of the lung represents a distinct clinicopathologic disease.