Alveolar-Cell Carcinoma (Terminal Bronchiolar Carcinoma)

The lesion variously described as alveolar-cell carcinoma, bronchiolo-alveolar carcinoma, and terminal bronchiolar carcinoma is a primary pulmonary neoplasm of relatively infrequent occurrence. In an operable case the tumor is typically peripheral. It may involve a small area of pulmonary parenchyma or it may be extensive, involving an entire lobe or all of a lung. In contrast to most bronchogenic carcinomas, this tumor, on gross examination, appears to arise from the pulmonary parenchyma rather than from a major bronchus. The microscopic finding of papillary neoplastic transformation of the lining mucosa of terminal bronchioles, in many cases, suggests an origin from terminal bronchiolar epithelium. The exact definition of alveolar-cell carcinoma and its relationship to ordinary adenocarcinoma of the lung have been a subject of some dispute. Some authors have used the term “terminal bronchiolar carcinoma” to cover a large number of peripheral adenocarcinomas of the lung, including those with much infiltration and reactive fibrosis. Others have restricted the designation to those peripheral tumors that are largely well differentiated and glandular, for which the walls of the distal air spaces serve as supportive stroma. In general, poorly differentiated adenocarcinomas of the lung show little tendency to line alveoli and, therefore, are usually classified as adenocarcinoma of ordinary type. Many other tumors, somewhat more differentiated, exhibit this tendency to some degree, particularly at their peripheries. At the Mayo Clinic, the designation “alveolar-cell carcinoma” is used only when all or the great bulk of the tumor shows this unique form of intrapulmonary dissemination, that is, the tendency to line alveoli. The definition is not unduly strict, for the term can be used in many otherwise typical cases in which the tumor contains small foci of reactive fibrosis or permeation of lymphatics. A review of the literature of alveolar-cell carcinoma also reveals some difference of opinion regarding prognosis. Davis and associates (1) and Decker (2) stated that the outcome was uniformly unfavorable. Mears and co-workers (5) reported that only 4 of 13 patients were alive at the time of follow-up, and that 2 of the 4 had recurrent tumors. On the other hand, the experience of Overholt and co-workers (6), Storey (9), and Smith and co-workers (8) was more favorable. They believed that, with early diagnosis and treatment, the prognosis was at least as good as for other forms of bronchogenic carcinoma. Since an earlier report from the Mayo Clinic (5), a larger proportion of small tumors has been encountered in our surgical material. In order to determine whether the size of the primary lesion had any bearing on prognosis, we reviewed all of our surgically excised alveolar-cell tumors. Materials and Methods