Abstract
BACKGROUND: Thymic malignancies are rare and there are limited contemporary population-based epidemiological studies for this uncommon cancer. PATIENTS AND METHODS: Adults aged 20 years and older diagnosed with thymic malignancies between 1988 and 2015 were identified from the California Cancer Registry (n = 1588). Trends in age-adjusted incidence rates were examined overall and according to race/ethnicity, and the proportion diagnosed according to stage was evaluated over time. Cox proportional hazards regression was used to estimate hazard ratios (HRs) for overall survival (OS), and Fine and Gray competing risks regression for cause-specific survival (CSS). RESULTS: Age-adjusted incidence increased on average 2.08% per year over the study period (95% confidence interval [CI], 1.30%-2.86%; P < .0001), with an incidence of 0.277 cases per 100,000 in 2015. Incidence was highest among Asian/Pacific Islander and non-Hispanic black individuals. The proportion of unknown stage at diagnosis declined as localized diagnoses increased over time. Compared with patients with thymoma, those with thymic carcinoma had significantly worse OS (HR, 1.63; 95% CI, 1.33-2.01; P < .0001) and CSS (subdistribution HR, 2.99; 95% CI, 2.29-3.91; P < .0001). Advanced stage at diagnosis was also associated with worse survival. Surgical intervention was associated with better prognosis for patients with localized (HR, 0.08; 95% CI, 0.02-0.30; P = .0002) or regional disease (HR, 0.14; 95% CI, 0.06-0.34; P < .0001). CONCLUSION: Thymic malignancy incidence is increasing in California. There was incidence variation across race/ethnicity, which warrants future study. These findings provide contemporary insight into the incidence and prognostic factors of thymic malignancies.