Is diffuse and peritumoral lymphocyte infiltration in papillary thyroid cancer a marker of good prognosis?

Papillary thyroid carcinoma (PTC) is the most frequently diagnosed endocrine neoplasia, representing 70 to 80% of all diagnosed thyroid cancers. Furthermore, Hashimoto's thyroiditis is a frequent inflammatory thyroid disease and the main cause of hypothyroidism. The relationship between Hashimoto's thyroiditis and PTC remains controversial.

Surgery for PTC was performed at our institution on 157 consecutive patients. They were classified by the degree of lymphocyte infiltration (LI). LI was classified as diffuse LI or peritumoral LI (only in or around the tumor), or absent. In addition, age, gender, tumor size, histopathological findings, lymph-node metastasis, extra- thyroidal extension, multifocal tumor, coexistence of LI and clinical outcomes were analyzed.

Out of the 141 patients included in the study, 83 (59%) had diffuse LI and 22 (16%) had peritumoral LI. In 36 patients (25%) LI was absent. A comparison of patients in the 3 groups revealed no significant difference in their genders, ages, smoking status, thyroid function, or nodule size at the time of surgery. The characteristics of PTC showed no differences in lymph-node metastasis, tumor invasion into contiguous neck structures, angioinvasion, or PTC subtypes. Tumor-node-metastasis (TNM) classification and classes did not differ among the 3 groups. During the follow-up, 64 out of 141 patients with PTC (55%) had recurrences from 6 to 130 months after the initial treatment. After a mean follow-up period of 8 yr we observed a significantly (p=0.01) high recurrence (66.6%) in the LI absent group with 24 of 36 patients when compared to patients from the diffuse LI group (32 out of 83 patients; 38.5%) and peritumoral LI group (8 out of 22 patients; 25%).

Although the role of the inflammatory-immune cells is complex and little understood, we found a more favorable course of PTC in the presence of LI (diffuse or peritumoral); this supports the hypothesis that LI represents a form of immune reaction to control tumor growth and proliferation.