Thymoma is associated with an increased risk of second malignancy

BACKGROUND. An association between thymoma and second malignancy has been suggested but has not been validated. Whether the relation is due to treatment or to other thymoma-associated conditions is unclear. METHODS. The authors studied 192 consecutive patients with thymoma and compared the incidence of second malignancies with those of 206 patients who underwent thymectomy for nonthymomatous conditions and 1426 patients with nasopharyngeal carcinoma (NPC). Detailed clinicopathologic features of thymoma patients with second malignancies were described. RESULTS. Additional malignancies were detected in 15 of 192 patients (8%) during their clinical courses. The risk for those patients was significantly greater compared with the risk for patients with nonthymomatous conditions (adjusted odds ratio [OR], 3.81; 95% confidential intervals [95%CI], 1.05-13.81; P = 0.042) and patients with NPC (adjusted OR, 4.89; 95%CI, 2.26-10.53; P <0.0001) after adjustment for age, gender, length of follow-up, myasthenia gravis, and radiation therapy. The occurrence of second malignancies did not correlate with histologic type or stage of thymoma, radiation therapy, or myasthenia gravis. CONCLUSIONS. Thymoma is associated with an increased risk of second malignancy. The association cannot be attributed to the effect of thymectomy or radiation therapy. Patients with thymoma, even if it is benign, should be followed regularly to facilitate the early detection of other malignancies.