Molecular-based diagnosis of
thyroid carcinomas can be more easily established by utilizing specific mRNAs that are expressed only in
cancer tissues. In a previous study, we introduced a new method of preoperatively diagnosing
thyroid carcinomas. This technique, aspiration biopsy-RT-PCR(ABRP), facilitated simultaneous cytological and molecular-based diagnoses by extracting
RNA from cells remaining within the needle used for fine needle aspiration biopsies(FNABs). ABRP provides both
RNA information and a cytological diagnosis without further invasion to the patient. We proved that by ABRP detection of
oncofetal fibronectin(onfFN)
mRNA in FNABs, papillary and
anaplastic carcinomas are accurately diagnosed preoperatively. Further, by real-time monitoring RT-PCR measuring onfFN
mRNA, a fully automated system was established. It is not clarified, however, why
cancer-specific mRNAs, especially those overexpressed in fetal tissues, can clearly distinguish benign tissues from
carcinomas, while genomic alternation such as mutations in RAS or P53 gene cannot. Further, a widely accepted hypothesis, multi-step
carcinogenesis, does not explain some of the clinical and experimental evidence from
thyroid carcinomas. Considering these facts, we propose a new concept of thyroid
carcinogenesis called "germ-cell
carcinogenesis", in which
cancer cells are derived from the remnant of fetal thyroid germ cells(thyroblasts) instead of normal thyroid follicular cells.