PURPOSE: Stable chromosomal aberrations (SCAs) have been found in circulating lymphocytes from patients treated for breast carcinoma. Therefore, we tried to define their incidence in such patients, to determine an in vitro dose-effect relationship, and to correlate these data with clinical parameters.
METHODS AND MATERIALS: This prospective study included 25 patients who, after surgery, underwent either radiotherapy (RT) alone (n = 15) or RT combined with chemotherapy (n = 10). SCAs were scored using the fluorescent in situ hybridization technique before RT and 4 and 12 months after RT. Dose-effect curves were established by in vitro irradiation of blood samples with 2 and 4 Gy, before and after treatment.
RESULTS: In all patients, the rate of SCAs increased significantly after external irradiation. No significant decrease in SCAs was observed during the first year after RT. RT and chemotherapy had no effect on the lymphocyte in vitro dose-effect relationship. No relationship was found in the distribution of patients between the yield of SCAs scored after external irradiation and after in vitro irradiation. SCAs after RT or in vitro irradiation did not correlate with family history of breast carcinoma or acute toxicity of treatment. More significantly, the yield of SCA after external irradiation was strongly related to the irradiation of the internal mammary chain and the supraclavicular lymph node area, suggesting that the volume of irradiated blood vessels was an essential parameter in determining the rate of SCAs.
CONCLUSION: A high and stable yield of SCAs persisted at least 1 year after external irradiation. The nature of the volume irradiated containing large blood vessels was the major determinant of the observed biologic dose.