Chronic lymphocytic thyroiditis (CLT) has a positive prognostic value in papillary thyroid cancer (PTC) patients: the potential key role of Foxp3+T lymphocytes.

Abstract

An impact of chronic lymphocytic thyroiditis (CLT) on papillary thyroid cancer (PTC) outcome has long been advocated but it is still controversial. The aim of this study was to evaluate the prognostic value of CLT in a retrospective cohort of PTC patients and to characterize the lymphocytic subpopulations and infiltrate (LI). We assessed 375 PTC patients, aged 45.2±16.4years, and treated with thyroidectomy and radioiodine remnant ablation, with a mean follow-up of 6.28±3.86years. In a subgroup of patients (n=81) tissue sections were reviewed for the presence of CLT or lymphocytes associated with tumor in absence of background thyroiditis (TAL); cytotoxic CD8+/regulatory Foxp3+T lymphocyte (CD8+/Foxp3+) ratio was characterized by immunohistochemistry: a low ratio is suggestive of a less effective anti tumor immune response. Seventy-five/375 patients (20%) had a histological diagnosis of CLT and showed at the last follow-up a significantly better outcome compared to those with no CLT (cure rate: 91.8 versus 76.3%, p=0.003). LI was characterized in 81 PTC patients (24 with CLT and 57 with TAL): the peri-tumoral CD8+/Foxp3+ratio was lower in patients not cured at the final evaluation. Our data suggest that concurrent CLT has a protective effect on PTC outcome and that the imbalance between cytotoxic and regulatory T lymphocytes in the peri-tumoral TAL may affect the tumor-specific immune response favoring a more aggressive behavior of cancer.