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

Background: An impact of chronic lymphocytic thyroiditis (CLT) on papillary thyroid cancer (PTC) outcome has long been advocated but it is still controversial. Purpose: 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). Materials and methods: We assessed 375 PTC patients, aged 45.2 ± 16.4 years, and treated with thyroidectomy and radioiodine remnant ablation, with a mean follow-up of 6.28 ± 3.86 years. 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. Results: 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. Conclusions: 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.