Metastatic Malignant Thymoma to the Abdomen: A SEER Database Review and Assessment of Treatment Strategies.

Background: Thymoma is a neoplasm occurring in 0.15 of 100,000 persons/year. Abdominal metastases are rare. We report the incidence of malignant thymoma (MT) and suggest imaging and treatment options for cases of abdominal metastasis.

Methods: A National Cancer Institute's Surveillance, Epidemiology and End Results database review was conducted to identify MT cases, followed by a literature review examining cases of metastases to the abdomen. Incidence rates were calculated, and symptoms, treatments, size and location of tumors, disease-free interval (DFI), and survival time were recorded.

Results: From 1973 to 2008, a total of 1,588 MT cases were identified (45.4 cases/year), which were extrapolated to 2,724 over 60 years. Incidence has risen from 17 cases in 1973 to 90 cases in 2008, with a larger incidence in males than females (0.23 vs. 0.17 per 100,000). There were 25 cases of abdominal metastasis (0.92%), 13 of which were asymptomatic. There was a wide variety of DFI and survival noted amongst the case reports. Multiple treatment modalities were used.

Conclusions: The incidence of MT is on the rise with a male predominance. All patients should receive routine imaging to look for extrathoracic metastases as half will not have symptoms. All patients with abdominal metastases should be treated using a multimodal approach.