Bronchioloalveolar carcinomas. Cell types, patterns of growth, and prognostic correlates.

Forty-five bronchioloalveolar carcinomas were studied, including 27 cases by electron microscopy. Bronchioloalveolar carcinomas can be classified by routine sections or by diastase-digested periodic acid-Schiff (PAS) stains, but electron microscopy is useful in confirming Clara cell or type II pneumocyte (nonmucinous) differentiation and excluding metastases. Mucinous bronchioloalveolar carcinoma can mimic metastatic adenocarcinoma histologically and ultrastructurally. Of the nine tumors with mucinous differentiation, eight had aerogenous dissemination (multifocal or with pneumonic spread), and seven of those eight were fatal. Twenty-four of 36 nonmucinous bronchioloalveolar tumors had aerogenous spread; all of the 24 patients died or were living with distant metastases. The 12 nonmucinous tumors without aerogenous dissemination had a 5-year survival rate of 61%. Among these, the smaller tumors had a better prognosis. The presence of alveolar spread, rather than cell type, was the most important feature predicting survival.