Involucrin in well-differentiated adenocarcinoma of the lung. Comparison with adenocarcinomas of different organs.

Using immunoperoxidase stain for involucrin, 50 well-differentiated adenocarcinomas of the lung were compared with similarly well-differentiated adenocarcinomas of other organs, 30 from the stomach, 30 from the colon, 12 from the pancreas and 12 from the prostate. Thirty (60%) adenocarcinomas of the lung were positive for involucrin; in 24 of 30 cases from 10% to more than 60% of tumor cells were positive and in the remaining 6 cases a few cells were positive. The positive cells included columnar or cuboidal tumor cells as well as some squamoid tumor cells. In contrast, only 4 (4.8%) of 84 tumors in the other organs were involucrin positive. Most of the involucrin positive foci of these four cases seemed to show squamous differentiation. These findings suggest that pulmonary adenocarcinoma is more prone to show squamous differentiation, compared with gastric, colonic, pancreatic and prostatic adenocarcinomas. The result may be applied for the differential diagnosis between primary and metastatic well-differentiated adenocarcinomas in the lung.