Transformation of thyroid epithelium is associated with loss of c-kit receptor

The receptor for the stem cell factor encoded by the c-kit proto-oncogene is expressed by a number of epithelial cells including thyrocytes. Since malignant transformation may be associated with loss of this receptor (melanoma and breast cancer), we have analyzed its expression in benign (38 cases) and malignant (31 cases) thyroid lesions. While low levels of c-kit are expressed in normal thyroids and in 60% of benign lesions, the receptor is undetectable in 60 and 90% of the follicular and papillary carcinomas, respectively. Northern blot analysis from surgical specimens of carcinomas and from carcinoma cell lines has demonstrated a lack of specific c-kit transcripts. These findings indicate that the c-kit receptor may be involved in the growth control of thyroid epithelium and that this function may be lost following malignant transformation.