Thyroid follicular oncogenesis in iodine-deficient and iodine-sufficient areas: Search for alterations of the ras, met and bFGF oncogenes and of the Rb anti-oncogene

Abstract

To gain insights into the role of iodine deficiency in favoring thyroid tumorigenesis (particularly of the follicular histotype), 22 Sicilian patients with thyroid tumors were selected for having lived permanently in either one of two areas of different iodine availability. Eleven patients (age 46.1 ±14.6 years, mean±SD; 10 females and 1 male) were from the iodine-deficient (ID) areas of the provinces of Messina and Catania (mean urinary excretion of iodine=48.1 µg/2A hours). Thyroid tumors were follicular or Hürthle cell adenomas (no.=3), follicular carcinomas (FC, no.=4), papillary carcinomas (PC, no.=2) and anaplastic carcinomas (no.=2). Eleven patients (age 47.1±15.2 years; 10 females and 1 male) were from the metropolitan area of Messina, an area of relative iodine-sufficiency (IS) (urinary excretion of iodine=95.2 µg/24 hours). These 11 patients had serum levels of TSH that were significantly lower than the corresponding values of the 11 patients from the ID area (0.76±0.33 vs 1.80±1.22 mU/l, p=0.01) The tumors of the 11 patients from the IS area were: follicular or Hürthle cell adenomas (no.=6), Hürthle cell carcinoma (no.=1), FC (no.=2), PC (no.=2). Molecular biology studies revealed that both the normal as well as the tumor tissue of all 22 patients did not harbor any of the three classical activating mutations (codons 12, 13 and 61) in any of the three ras oncogenes. Similar negative results were obtained as far as loss of heterozygosity of the retinoblastoma (Rb) anti-oncogene is concerned. Immunohistochemistry studies were performed to investigate expression of c-met and basic fibroblast growth factor (bFGF) proto-oncogenes. Only one Hürthle cell carcinoma and the two PC from the IS group, and one FC and the two PC from the ID group stained for the c-met oncogene. Expression of c-met was greater (3+) in the four PC (concerning 70–80% of the tumor cells) than in the other two cancers (1+; <5% of the tumor cells). In the IS group, positivity for bFGF was detected in 3/6 adenomas, 1/2 FC, the Hürthle cell carcinoma and the two PC. In the ID group, positivity for bFGF was observed in 2/3 adenomas, 2/4 FC, the two PC and the two anaplastic carcinomas. The 8 positive cases from the ID group had a greater level of bFGF expression than the 7 positive cases from the IS group (intensity of staining = 2.0+ vs 1.57+). Interestingly, the greatest expression of bFGF was seen in the cases with peri-tumoral lymphocytic infiltration from either group. In the ID group correlations between (i.) pre-intervention serum TSH and intensity of tumoral staining for bFGF, (ii.) serum TSH and per cent of tumoral cells reactive with anti-bFGF and (iii.) between intensity of staining for bFGF and per cent of tumoral cells bFGF +ve were higher than in the IS group. We conclude that activating mutations of ras, loss of DNA from the Rb locus and over-expression of both c-met and bFGF are of no pathogenetic relevance in driving thyroid tumorigenesis of iodine-deficient areas.