Lung carcinoma mimicking malignant lymphoma: report of three cases.

Three cases of lung carcinomas with unusual histologic appearances that have received little or no comment in the literature are presented. They were initially confused with malignant lymphoma because of a diffuse proliferation of relatively monotonous cells simulating large-cell immunoblastic lymphoma. In each case, the possibility of malignant lymphoma was excluded with confidence after the immunohistochemical study (leucocyte common antigen negative and cytokeratins positive), although with conventional microscopy several foci of cohesive groups of tumor cells were observed. The tumors were ranked at the clinical stage II or III when they were initially discovered, but all patients died of disease within 1 year. The present three tumors show an aggressive behavior and could be classified into a peculiar variant of 'large cell' carcinoma. It is necessary for surgical pathologists to have an idea of these variants of lung carcinoma in order to avoid erroneous diagnosis.