The risk of second primary malignancy in patients with localized thymoma: A U.S. population-based study.

Abstract

8568 Background: Thymoma is a rare neoplasm of anterior mediastinum. Patients often have an indolent disease. The prognosis of limited stage disease is excellent with a 10-year survival rate of 70 to 80%. Data regarding the risk of second primary malignancy in thymoma survivors are limited in recent years. In this study, we aimed to determine the risk of second primary malignancies (SPMs) among patients with limited stage thymoma. Methods: We utilized the Surveillance, Epidemiology and End Results (SEER)-13 registry to identify adult patients (≥ 18 years) with limited stage thymoma. We calculated the risk of SPM, developing ≥ 6 months after an index thymoma diagnosis, using Multiple Primary Standardized Incidence Ratio and an Absolute Excess Risk (AER) between 2004 and 2010. Statistical significance was defined as p < 0.05. Results: The database identified a cohort of 1,544 patients with limited stage thymoma with a median follow-up duration of 107 months (11-281 months). A total of 176 (11.39%) patients developed SPMs with a median latency of 62.5 months (range 6-272 months). Median age at diagnosis of SPM was 69 years (range 25- 96 years). Overall, SPM occurred at an observed to expected (O/E) ratio of 1.53 (95% CI 1.32-1.76), p < 0.001 with an AER of 60.52 per 10,000 patient-years at risk. A significantly increased risk was noted for cancer of lung and bronchus (O/E 1.77, 95% CI 1.21-2.52, p = 0.004; AER 12.17/10,000), skin excluding basal and squamous (O/E 2.09, 95% CI 1.04-3.75, p = 0.03; AER 5.17/10,000), urinary bladder (O/E 2.14, 95% CI 1.17-3.6, p = 0.014; AER 6.72/10,000), thyroid (O/E 3.48, 95% CI 1.4-7.17,p = 0.009; AER 4.49/10,000), and leukemia (O/E 3.26, 95% CI 1.63-5.83, p = 0.001; AER 6.86/10,000), including acute lymphocytic leukemia (O/E 16.09, CI: 1.95-58.11; AER 1.69/10,000), acute myeloid leukemia (O/E 3.83, CI: 1.04-9.8; AER 2.66/10,000) and other acute leukemia (O/E 29.45, CI: 3.57-106.39; AER 1.74/10,000). The risk was not significant for lymphoma (Hodgkin and non-Hodgkin), chronic leukemia, oropharyngeal, digestive tract and hepatobiliary cancer as SPM. Conclusions: The risk for SPMs is significantly increased in patient with thymoma compared to general population. Given the long-term risk of SPM, patient should be followed closely with judicious use of age-appropriate cancer screening.