The pathobiologic features of carcinomas of type II pneumocytes. An immunocytologic study.

Adenocarcinomas of the lung without squamous differentiation or obvious mucus production from 51 patients were studied. Twenty-eight tumors (55%), when stained with rabbit anti-human surfactant apoprotein antiserum by the peroxidase-antiperoxidase method, demonstrated characteristic nuclear inclusions. Most of these tumors could be identified histochemically by the presence of eosinophilic, periodic acid-Schiff (PAS)-positive nuclear inclusions. In patients with apoprotein-immunoreactive tumors there were nine deaths due to tumor (32%) within 5 years of diagnosis. Eight of the nine deaths occurred in patients whose tumors exceeded 3 cm in diameter; an equal number of patients were smokers. The average age of patients with apoprotein-positive tumors was 67.3 years, a figure greater than that for patients with apoprotein-negative tumors (61.4 years). Five of the 23 patients with apoprotein-negative tumors died of their neoplasms; in two of the subjects the tumors exceeded 3 cm in diameter. In that no significant difference in survival was observed in patients with apoprotein-positive and apoprotein-negative tumors, it was concluded that subclassification of adenocarcinomas of the lung as apoprotein-positive, i.e., type II pneumocytic, or as apoprotein-negative, is of no clinical or prognostic significance. Nonetheless, peripheral tumors measuring less than 3 cm in size and showing neither squamous differentiation nor obvious mucus production should be recognized as a prognostically favorable group in comparison with other types of lung carcinomas.