Scar carcinoma of the lung: a historical perspective.

Lung scar carcinoma (SC) was first described by Friedrich in 1939 as a type of lung cancer that originates around peripheral scars in the lung. Scarring in the lung can result from a variety of infections, injuries, and lung diseases. Scars can also be due to repeated episodes of tumor necrosis and healing. SCs are typically found as subpleural adenocarcinomas with retraction or puckering of the overlying pleura. They were considered a histologic curiosity that was promoted for decades until doubts about their existence were raised in the 1980s. Finding type III collagen, type V collagen, and myofibroblasts characteristic of fibrosis in the scars, finally reversed the original SC concept. The presence of type III collagen and extracellular matrix suggested an ongoing fibrosing process secondary to host response to the neoplasm. The high concentration of type III collagen in SC indicates that the fibrous tissue is in an active immature state compared with noneuplastic fibrous tissue, which is mature and contains type I and type V collagen. A recent cohort analysis of data from the PLCO (Prostate, Lung, Colorectal and Ovarian) cancer screening trial demonstrated a correlation between the presence of scar and the development of carcinoma, but the causation of this association has to be determined by future studies. The role of inflammation, infections, and smoking in the development of cancer is discussed in this article. Additional research is necessary to determine if lung scarring detected by imaging requires clinical monitoring in the context of the development of lung cancer when a defined set of risk factors is identified.