Increased Incidental Thyroid Cancer in Patients With Subclinical Chronic Lymphocytic Thyroiditis

The autoimmune process and increased TSH associated with chronic lymphocytic thyroiditis (CLT) are factors that may promote development of thyroid cancer. When surgically removed, the cellular changes of CLT are commonly seen surrounding thyroid cancers. This study investigates the malignancy rate in CLT patients when compared with non-CLT patients after thyroidectomy.

A retrospective review of prospectively collected data for 1268 patients with index thyroid nodules who underwent thyroidectomy at a single institution was performed. Patients were excluded if they had previous thyroid surgery, known thyroid cancer, Graves' disease, family history of thyroid cancer, and history of radiation exposure. Patients were subdivided into CLT and non-CLT groups by final pathology. Final pathology was reviewed and grouped into cancer in the index thyroid nodule and incidental thyroid cancers. Chi-squared analyses were performed using SAS.

Of 359 patients that met study criteria, 52 had CLT. Overall, the malignancy rate was 37% in both CLT patients (19/52) and non-CLT patients (114/307) (P = 0.86). However, incidental thyroid cancer was found in 15% (8/52) of CLT patients and 10% (31/307) of non-CLT patients (relative risk = 1.52) who had no index nodule cancer. The breakdown of incidental cancer subtype in CLT patients was classic variant papillary thyroid carcinoma (PTC), n = 3; follicular variant PTC, n = 5.

Patients with CLT have a 1.5-fold increased risk of incidental PTC. CLT should be considered a risk factor for incidental thyroid cancer, and patients with this thyroid condition should be counseled and monitored periodically for underlying thyroid malignancy.