Thyroid hormone receptor [beta]1 in normal colon and colorectal cancer- association with differentiation, polypoid growth type and K-ras mutations

The precursors for colorectal cancer include polypoid (conventional), flat and serrated adenomas. Polypoid growth in polypoid adenomas and serrated adenomas is associated with K-ras mutations. The regulation of polypoid or nonpolypoid growth is not well known, but could be related to trophic stimuli, such as thyroid hormones. Hence, we investigated the expression pattern of thyroid hormone receptor TR[beta]1 in colorectal mucosa and in colorectal tumours and its relationship to tumour growth type. One hundred fourteen colorectal carcinoma specimens were evaluated for TR[beta]1. Normal mucosa, adjacent adenomatous component (N = 46) and lymph node metastases (N = 28) were analysed when present, and the results were confirmed by Western blot analysis in selected cases. Nuclear TR[beta]1 was almost always present in normal epithelium (96%), but less frequent in adenomas (83%) and in cancer (68%; p < 0.001 and p < 0.001, respectively). TR[beta]1 was associated with polypoid growth, presence of K-ras mutations and also with a higher WHO histological grade and advanced Dukes' stage. Cytoplasmic expression of TR[beta]1 was observed in nonneoplastic and neoplastic epithelium. In Western blot analysis, a 58 kDa band corresponding to TR[beta]1 was expressed in normal mucosa and in colorectal cancer specimens with positive immunohistochemistry. Association of TR[beta]1 expression with growth pattern and the presence of K- ras mutations suggest that abnormalities in thyroid hormone signalling involving TR[beta]1 play a role in the development of some types of colorectal adenocarcinomas.