The possible role of radiotherapy in chronic lymphocytic leukaemia: a critical review.

The few clinical studies which have utilized irradiation as a treatment modality for chronic lymphocytic leukaemia (CLL) during the last two decades have led to rather conflicting and sometimes disappointing results. Low-dose total body irradiation (TBI) and extracorporeal, or mediastinal, radiotherapy did not appear to be superior to chemotherapy in most trials. Only the fractionated low-dose (600-800 rad) splenic irradiation was found to induce a long-lasting decrease of the lymphocyte count and a decrease in bone marrow infiltration in a significant proportion of cases, without any noticeable haematological toxicity. But new data is recently emerging; stratification of CLL in various subgroups, better understanding of the role of the normal T-cell subsets, better knowledge of the interaction between irradiation and haematopoiesis, and of the radiosensitivity of the various lymphocyte subpopulations. Thus one can now reconsider the possible role radiotherapy, and particularly splenic irradiation, can play as an alternative treatment to chemotherapy for CLL. Haematological toxicity is still limiting the use of TBI. The spleen irradiation avoids this drawback. Recent data suggest that this splenic irradiation could be efficient by means of several mechanisms; the successive destruction, fraction after fraction, of the part of the malignant lymphocyte clone present in the spleen is likely to be the main therapeutic explanation, with the knowledge that the lower the differentiation of the malignant clone, the more efficacious the irradiation. But in parallel, the destruction of the large subset of T-suppressors which is constantly present in the spleen may account for the improvement of the peripheral blood count after splenic irradiation, and possibly for a direct effect towards the malignant clone. With respect to these new data, splenic irradiation clearly needs further clinical evaluation in the treatment of CLL.