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.