Influence of Smoking and Histologic Subtype on Developing Extrathymic Malignancy in Thymoma Patients

Patients with thymomas are at high risk of developing extrathymic malignancies. We investigated the impact of extrathymic malignancies on the prognosis of patients with thymoma who underwent surgery and the risk factors for postoperative extrathymic malignancies.

A multicenter retrospective review of 252 patients who underwent surgical resection of thymomas from January 1977 to March 2016 was conducted. The exclusion criteria were recurrent thymoma, rare types of thymoma, and missing data. The overall number and incidence of extrathymic malignancies were calculated. Potential predictors of extrathymic malignancies were also evaluated.

Two hundred twenty-eight patients were analyzed. Fifty-five extrathymic malignancies were observed (23 postoperative, 8 synchronous, and 24 preoperative). Among the overall cohort, the incidence of extrathymic malignancies significantly increased the patients' risk of death (hazard ratio [HR], 4.02; 95% confidence interval [CI], 1.72 to 9.40; p < 0.01). Among patients aged less than 70 years, the incidence of extrathymic malignancies was an independent risk factor for death. The incidence of postoperative extrathymic malignancies was significantly higher in patients with indolent forms of thymoma (type A/AB/B1) than aggressive forms (type B2/B3) (p = 0.02). In the multivariate analysis, indolent forms of thymoma (type A/AB/B1) (HR, 4.03; 95% CI, 1.12 to 14.6, p = 0.03) and a history of ever having smoked (HR, 5.29; 95% CI, 1.30 to 21.6; p = 0.02) were significant risk factors for the cumulative incidence of postoperative extrathymic malignancies.

Extrathymic malignancies increased the risk of death in patients with thymomas. Indolent forms of thymoma and a history of ever having smoked were risk factors for postoperative extrathymic malignancies.