Brain irradiation-induced lymphocytosis predicts response in cancer patients with brain metastases

Lymphocytopenia is one of the main toxicities of radiotherapy and its severity is related to the irradiation dose. The occurrence of lymphocytopenia depends on the body site of radiotherapy; it is most pronounced with pelvic irradiation, whereas the effect of brain irradiation on the lymphocyte count is to be elucidated. This preliminary study was performed to evaluate changes in lymphocyte number occurring during brain irradiation in cancer patients with brain metastases. The study included 50 patients who received brain radiotherapy for single or multiple brain metastases at a total dose of 30 Gy. Overall, no significant changes in mean lymphocyte number occurred during brain radiotherapy. However, when lymphocyte variations were assessed in relation to the clinical response of brain metastases, a significant increase in the mean number of lymphocytes was found in patients who achieved objective regression of brain metastases on brain irradiation. The mean lymphocyte number decreased in nonresponding patients, albeit without a statistically significant difference with respect to the pretreatment values. The results of this study show that the efficacy of radiotherapy in the treatment of brain metastases is associated with a significant increase in mean lymphocyte number. Therefore, evidence of brain irradiation-induced lymphocytosis may predict the efficacy of radiotherapy.