BRAF^V600E, hypothyroidism, and human relaxin in thyroid carcinogenesis

BRAF^V600E, a major driver of thyroid cancer, evaluated in the context of thyroid hormones and human relaxin.

Immunohistochemical expressions of BRAF^V600E, TSH, TSH receptor (TSHR), T4, T3 receptor (T3R), RLNH2, and its receptor, RXFP1, were evaluated in thyroid tumors from a retrospective U.S. population of 481 cancer cases diagnosed in 1983-2004.

BRAF^V600E was expressed in 52% of all thyroid tumors; expression of other markers ranged from 25% for T4 to 98% for RLNH2. Tumors predominantly exhibited hypothyroid-like conditions characterized by elevated TSH and TSHR and reduced T4. BRAF^V600E prevalence was significantly higher in tumors expressing TSH, TSHR, T3R, and RXFP1 and lower in tumors expressing T4. The proportion of BRAF^V600E mutation in classic papillary tumors significantly increased from 56 to 72% over the 21-year period of diagnoses, while expression of RXFP1, TSH, TSHR, and T3R decreased in non-tumor. Racial/ethnic differences were observed in thyroid hormone marker expression. Non-tumor expression of TSH, TSHR, and T3R were each associated with shorter overall survival, but did not remain significant after adjustment for demographic and clinical factors.

Our study provides the first evidence of the potential interaction of BRAF^V600E mutation, relaxin, and thyroid hormones in thyroid carcinogenesis. Moreover, our results suggest that hypothyroidism, influenced by RLNH2 activity, may underlie the development of the majority of thyroid cancers and mediate the role of BRAF^V600E in thyroid carcinogenesis. BRAF^V600E mutation is increasing in papillary thyroid cancers and may be contributing to the rising incidence of this malignancy.