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Observations on Bronchiolo‐alveolar Carcinomas with Special Emphasis on Localized Lesions: A Clinicopathological, Ultrastructural, and Immunohistochemical Study of 11 Cases

Pathological and clinical features in early localized mucinous and nonmucinous bronchiolo-alveolar carcinomas (BAC) have not been adequately compared. In an attempt to characterize such lesions, we studied the clinicopathological, ultrastructural, and immunohistochemical features of three mucinous and eight nonmucinous BAC (four Clara cell, four Type II pneumocyte) along with one sheep pulmonary carcinoma (SPC). Tumor border, associated fibroplasia, tumor cell incohesion, lymphocytic infiltrate, T-lymphocytes, Langerhans cells (LC), and Leu-Mi and OC 125 immunoreactivity were evaluated. Localized tumors of both types had a similarly favorable prognosis, even when the tumor size was greater than 3 cm or showed more complex histology. Type II pneumocyte carcinomas with tumor cell disassociation and desquamation or a pseudomesotheliomatous phenotype did poorly. Clara cell and type II carcinomas elicited an LC and T-lymphocyte immune response. LC and T-lymphocytes were absent in mucinous BAC and SPC. All of the three mucinous and three of the seven nonmucinous BAC were Leu-Ml negative, indicating that Leu-Ml may not distinguish between BAC and mesothelioma, especially in a small biopsy specimen. Tumors with absent or slight Leu-Ml immunoreactivity had a favorable outcome irrespective of cell type and presence or absence of LC. Inasmuch as OC 125 was negative in all cases of BAC, OC 125 may be a useful adjunct in the immunodi-agnosis of mesothelioma. Our investigation supports the view that two different groups of tumors are assembled under the single nosologic entity of BAC: one, mucinous, which grows along an unaltered pulmonary alveolar framework and elicits a B-lymphocytic response, and the other, nonmucinous, which induces desmoplasia and elicits an LC and T-lymphocytic response. Only mucinous