Ectopic expression of c‐kit in small‐cell lung cancer

Accumulating evidence suggests that c‐kit plays an important role in the regulation of growth of at least 3 lineages of stem cells, while only very limited data are available on the development of human solid tumors. Our recent studies have shown that c‐kit transcripts are expressed in a very restricted sub‐set of human solid tumors such as small‐cell lung cancer (SCLC). We have also conducted an immunohistological study on in situ localization of the c‐Kit protein in various human solid tumors as well as in corresponding fetal and adult normal tissues. No c‐kit expression was detected in normal bronchial epithelial cells or pneumocytex in lung parenchyma of human fetal and adult specimens, indicating that the c‐kit protein is aberrantly expressed in lung‐cancer cells. We also found that significant chemotactic response as well as moderate in vitro cell growth occurred in SCLC cell lines upon addition of recombinant human stem‐cell factor.