The receptor for the stem cell factor encoded by the c-kit proto-oncog
ene is expressed by a number of epithelial cells including thyrocytes.
Since malignant transformation may be associated with loss of this re
ceptor (melanoma and breast cancer), we have analyzed its expression i
n benign (38 cases) and malignant (31 cases) thyroid lesions. While lo
w levels of c-kit are expressed in normal thyroids and in 60% of benig
n lesions, the receptor is undetectable in 60 and 90% of the follicula
r and papillary carcinomas, respectively. Northern blot analysis from
surgical specimens of carcinomas and from carcinoma cell lines has dem
onstrated a lack of specific c-kit transcripts. These findings indicat
e that the c-kit receptor may be involved in the growth control of thy
roid epithelium and that this function may be lost following malignant
transformation.