RISING INCIDENCE OF BRONCHIOLOALVEOLAR LUNG-CARCINOMA AND ITS UNIQUE CLINICOPATHOLOGICAL FEATURES

Background. Bronchioloalveolar lung carcinoma (BAC) is a unique type of lung cancer with distinguishing pathologic, biologic, epidemiologic, demographic, and perhaps etiologic features. Methods. The authors investigated and analyzed all of the cases of pathologically confirmed BAC seen at our institution in the hope of discovering new or confirming known features of this disease. Results. When cases of BAC expressed as a percentage of total lung cancers were analyzed in successive 5-year periods from 1955 to 1990, BAC rose from less than 5% to 24.0% (P < 0.001). Much of the increase in BAC occurred in women, as evidenced by a male-to-female ratio that wavered around unity. The mean age of BAC adenocarcinoma patients was 59.2 +/- 11.5 years, compared to 64.1 +/- 13.5 years for non-BAC adenocarcinoma (P < 0.05). BAC also contrasted with other forms of lung cancer by exhibiting a relatively high incidence of multifocality (25% versus 5%) (P < 0.001). There was an association between histologic subtype of BAC and pattern of pulmonic involvement. The mucinous subtype was more strongly associated with diffuse pulmonic involvement, and the sclerotic subtype was more strongly associated with multifocal involvement (P < 0.001). Furthermore, BAC cases exhibited a 20% incidence of dedifferentiation into patterns of poorly differentiated adenocarcinoma, a feature that was more associated with the mucinous and sclerotic subtypes (P < 0.05). Conclusions. The emergence of BAC as a prominent type of lung cancer should stimulate new basic laboratory and case-control studies to elucidate further the natural history and etiology of this unique disease.