Suspected immunosuppression and increased micronucleus frequency in patients with testicular seminoma 7 years after radiotherapy.

Abstract

e15075 Background: In addition to therapeutic efficiency and survival rate, the success of radiotherapy is also measured by side effects and long-term health risks. Secondary cancer incidence and immunosuppression are parameters in estimating the health risk of radiotherapy (RT) in seminoma patients (pts). Testicular seminoma pts undergo significant lymphocyte genome damage during and after radiotherapy. The aim of this study was to see if there is genome damage and immunosuppression detectible by micronucleus (MN) assay seven years after radiotherapy. Methods: This study followed up 10 testicular seminoma stage I pts aged 23-49 years who were analyzed for genome damage and mitotic index (MI) using the MN assay (Fenech, 1985) 7 years after tumour removal and RT with the total dose of 25 Gy/16 daily fractions. For reference 10 healthy, age-matched men was used. Statistical analysis of differences between the groups was performed by the Mann-Whitney U-test. Results: MN frequency in binuclear lymphocytes did not differ significantly between pts and controls (6.03/1000 vs. 4.70/1000 cells; P<0.05). Patients showed a significantly higher MN frequency in mononuclear lymphocytes (2.88/1000 vs. 0.33/1000; P<0.05 ). In addition, their MI was significantly lower than in controls (1.19 vs 1.50; P<0.05). Conclusions: This is the first study to show increased MN frequency in mononuclear lymphocytes of testicular seminoma pts 7 years after radiotherapy. Our study stresses the significance of scoring MN frequency in both mono and binuclear lymphocytes in order to avoid false findings. Detected genome instability may be related with possible secondary cancer risk. Disturbances in the mitotic apparatus and suspected immunosuppression, expressed as low MI, suggest that it is necessary to run also immunologic surveillance of cancer pts after RT. As phytohaemagglutinin is used for stimulation of T lymphocyte proliferation in MN assay, our findings of decreased MI are in concordance with depletion of CD 4 T lymphocytes reported in survivors of nuclear bomb. Future studies should investigate the possible differences in radiosensitivity between lymphocyte subtypes in these pts and health risks they involve.