In vivo somatic mutation in the lymphocytes of Hodgkin's disease patients

While current medical therapies for Hodgkin's disease are usually quite effective, it has become increasingly clear that some of the therapies utilized carry an inherent risk for the induction of secondary malignancies. In order to examine the cellular and genetic responses to therapy for Hodgkin's disease among individuals, we have determined the mutant frequency of T‐lymphocytes in 3 cohorts of patients (N = 86) and in controls (N = 71) using a T‐cell cloning assay selecting for 6‐thioguanine resistance. The Hodgkin's disease cohorts studied include 1) new and untreated, 2) radiotherapy, and 3) combined modality therapy patients. Additionally, two patients receiving chemotherapy alone were studied. In untreated patients, 3 of 18 (17%) mutant frequencies were above the upper 95% confidence limit for mutant frequency in controls (12.6 × 10−6). After therapy, 14 out of 45 (31%) of those treated with X‐rays only and 10 of 23 (44%) patients treated with both X‐rays and chemotherapy had mutant frequencies greater than 12.6 × 10−6. Overall, the results indicated that the individual response to Hodgkin's disease therapy was a heterogeneous one with a sub‐population of persons having elevated mutant frequencies even many years after their last treatment. The larger frequency of elevated MFs in those patients who received intensive therapy (chemotherapy and radiotherapy) is consistent with their increased risk for second cancer induction.