Basement Membranes in Bronchogenic Squamous Cell Carcinoma: An Immunohistochemical and Ultrastructural Study

Basement membrane (BM) deposition at the interface of tumor cells and stroma was studied in 27 bronchogenic squamous cell carcinomas. Specimens from peripheral and central parts of each tumor were collected. These were frozen, formalin fixed and paraffin embedded or fixed in Karnovsky's fixative, and processed for electron microscopy. With the use of antibodies to type IV collagen and laminin, the BM was visualized by light microscopy with an indirect immunoperox-idase technique. Light microscopic findings were compared to ultrastructural observations. The peripheral parts of the tumors showed continuous BM in a recognizable preexisting alveolar pattern without evidence of invasive growth into the alveolar septa. In contrast, central parts showed highly variable BM deposition ranging from continuous to almost completely absent. Alveolar patterns were not observed in the tumor centers. The stromal compartment of the tumor centers contained many spindle cells with irregular pericellular BM-like material that could be identified ultrastructurally as myofibroblasts. Electron microscopy and immuno-histochemistry yielded virtually identical results. It is concluded that invasive growth in bronchogenic squamous cell carcinomas occurs in central parts of the tumor when the tumor periphery shows expansive growth without invasion of alveolar septa. The situation is different in invasive squamous cell carcinomas originating from other organs because of anatomical differences between the lung and solid organs.