Extrathymic malignancies associated with thymoma: a forty-year experience at a single institution.

Objectives: Patients with thymoma are reported to have an increased risk for developing second malignancies. The aim of this study was to assess the incidence of second malignancies among patients with thymoma. We focused especially on the impact that lung cancer has on survival in these patients.

Methods: Three hundred and thirty-five patients who underwent surgery for thymoma in Chiba University Hospital from January 1971 to November 2012 were included in this study. Patient records were reviewed retrospectively for data on background, treatment, second malignancies and clinical outcome.

Results: Fourteen patients had a history of malignancy until the time of operation, with an additional 20 diagnosed simultaneously with the thymoma. Forty-three malignant lesions in 33 patients were found post-thymectomy. Lung cancer was diagnosed in 17 patients, far exceeding the expected number in the cohort, which was calculated according to Japanese national data. The median survival time of the thymoma patients who had lung cancer at the time of surgery was 5.8 years. The survival of patients with thymoma and lung cancer was poor in comparison with that of others.

Conclusions: Secondary lung cancer is frequently found in thymoma patients and could be one of the factors limiting survival. We recommend an annual computed tomographic scan of the thorax to detect not only recurrent thymoma but also lung cancer at an early stage in order to improve the survival of these patients.