Bronchiolo-alveolar carcinoma with nuclear tubular inclusions. Case report and electron microscopy findings.

A case of bronchiolo-alveolar carcinoma with the ultrastructural characteristics of type II pneumocytes is presented. Tubular type nuclear inclusions were frequent. Two types of inclusions were seen: a common uncircumscribed type and a chromatin or cisterna demarcated type which resembled cytoplasmic pseudoinclusions. Both types, however, appear to be variants of the same lesion since intermediate or transitional forms can be observed. Inclusions of the same type were seen in cells from extrapulmonary metastases from this carcinoma. This excludes the possibility that cells with inclusions represented trapped non-neoplastic type II pneumocytes.