Image analysis quantitation of immunoreactive retinoblastoma protein in human thyroid neoplasms with a...

Studies investigating the molecular pathogenesis of common thyroid neoplasms have shown altered expression and/or structure of proto-oncogenes, G-proteins, and growth factors. Growth suppressor genes, genomic DNA segments that code for proteins believed to function as growth suppressors, have not been evaluated for a potential role in the pathogenesis of thyroid neoplasms. The retinoblastoma gene (RB1) maps to chromosome 13q14 and encodes a 110 kilodalton variably phosphorylated nuclear protein (Rb) that functions as a growth suppressor in a wide variety of human tissues. The frequent association of Rb protein loss with multiple neoplasms has prompted the authors to apply a specific and rapid immunohistochemical technique using streptavidin-biotin-peroxidase technology evaluated by image analysis that can be used to quantitate the level of immunoreactive Rb protein (iRb) in thyroid neoplasms. In utilizing streptavidin-biotin technology for nuclear iRb detection, artifacts that can be associated with the use of avidin such as nonspecific binding at physiologic pH and nonspecific complex formation with cellular components including chromatin are avoided. By this method, positive nuclear staining for iRb in the follicular cells of three follicular adenomas and in CV-1 control cells known to express Rb was demonstrated. Two papillary carcinomas, two medullary carcinomas and a SAOS-2 cell line known to produce a defective form of Rb stained at significantly lower levels (P less than .001). The authors conclude that the streptavidin-biotin-peroxidase staining technique evaluated by image analysis is a sensitive and specific detection system for nuclear iRb studies; has significant advantages over previously used techniques; and that thyroid neoplasms may variably express iRb which may, in part, reflect their variable pathogenesis.