Influence of lymphocytic thyroiditis on the prognostic outcome of patientswith papillary thyroid carcinoma

Both the association between lymphocytic thyroiditis (LT) and papillary thy roid carcinoma (PTC), and the prognostic significance of lymphocytic infilt rate in patients with thyroid malignancy, remain controversial. We examine the above relationships by retrospectively reviewing our series of patients treated for differentiated nonmedullary thyroid carcinoma at University of California-San Francisco over a 25-yr period (1970-1995). Of the 631 patie nts with complete data for analysis, 128 patients (20.3%) showed concomitan t histologic evidence of LT and 503 patients (79.7%) had no evidence of LT. Prognostic outcome was assessed using Kaplan-Meier survival plots and anal ysis of risk factors by Cox's proportional-hazard modeling. The cohort with LT revealed a higher frequency of PTC (97.7% vs. 87.3%) and female patient s (85.2% us. 66.8%), a lower frequency of extrathyroidal invasion (7.8% us. 23.3%) and nodal metastases (25.8% us. 43.3%), and absence of distant meta stases (0% vs. 4.8%), respectively, compared with those without LT. At init ial surgery, a significantly greater proportion of patients with LT belonge d to lower pathological tumor-node-metastasis stages, compared with those w ithout LT (stage 1, 86.7% vs. 73%; stage 2, 4.7% vs. 8.3%; stage 3, 8.6% vs . 15.3%; and stage 4, 0% us. 3.4%). Over a mean +/- SE follow-up period of 11.1 +/- 0.4 yr, patients with LT had significantly lower cancer recurrence rate (6.3% vs. 24.1%; P < 0.0001) and cancer mortality rate (0.8% us. 8.0% ; P = 0.001), respectively, compared with those without LT. In summary, our series showed a relatively common occurrence of LT in patients with PTC, a nd we believed that lymphocytic infiltration developed mainly in response t o the tumor itself. We also found a more favorable course of PTC in the pre sence of LT; this supports the hypothesis that lymphocytic infiltration rep resents a form of immune reaction to control tumor growth and proliferation .