Immunohistopathologic and biochemical studies of different collagen types extracted from human scar carcinoma of the lungs have been carried out for definition and evaluation of which types of collagen are involved in the scarring mechanism of such tumors. Tumor homogenates treated with 0.5 M acetic acid and followed by limited proteolysis with pepsin and then by fractional salt precipitation, demonstrated that Type I collagen constitutes the major collagenous component in addition to a significant increase in Type V collagen extracted from human scar carcinoma of the lung. However, when normal membranoalveolar peripheral lung tissues were processed under the same experimental conditions, Type III and IV collagens were relatively higher. Immunohistochemical studies were carried out, and the results confirmed the data above. Furthermore, these studies demonstrated a relative localized increase in Type III collagen in the area surrounding the tumor acini, which suggested that these areas are of active and recent scar formation. This supports the current concept of the scar origin as a desmoplastic reaction of the host tissues toward the neoplastic cell growth.
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