COEXISTENT THYROIDITIS IS ASSOCIATED WITH LOWER TUMOR STAGE IN THYROID-CARCINOMA

Background Microsatellite instability (MSI) is a new mechanism describ ed in carcinogenesis of several rumours and seems to predispose for ca ncer in some chronic inflammatory diseases. As thyroiditis is thought to be both the cause and the consequence of thyroid carcinoma, it was the aim of this retrospective study to investigate the epidemiology an d the influence of a coexistent thyroiditis on prognosis and clinicopa thological parameters in an iodine-deficient area. Methods The grade o f lymphocytic infiltration (LI) of 153 thyroid carcinomas was determin ed in paraffin-embedded tissues: G0=no LI, G1 = peritumoral LI, G2 = p eritumoral LI with follicle, G3 = diffuse LI. A non-radioactive PCR-ba sed screening method was used for detection of MSI. Results Twenty-sev en (17.7%) out of 153 carcinomas were accompanied by thyroiditis (GI, 16; G2, 5; G3, 6). Ten cases fulfilled the criteria necessary for diag nosing Hashimoto's thyroiditis. Nine out of 10 (90%) Hashimoto's cases and 16 out of 17 (94%) other thyroiditis cases were associated with a significantly (chi(2) < 0.01) lower pT stage (pT1, pT2) than cases wi thout thyroiditis. No statistical association was found by comparing m ultifocality or sclerosing variants with the grade of lymphocytic infi ltration. MSI was detected neither in patients with severe inflammatio n nor in the absence of thyroiditis. Conclusions MSI does not seem to play a role in the pathogenesis of thyroid carcinoma. Coexistent thyro iditis is associated with a lower pT stage and thus could be an indica tor of a better prognosis.