Radioimmunotherapy and autologous stem cell transplantation for the treatment of B-cell lymphomas

Relapse continues to be the primary cause of treatment failure in patients with non-Hodgkin's lymphomas (NHL) undergoing high-dose therapy and autologous stem cell transplantation. The anti-CD20 radioimmunoconjugates, Y-90 ibritumomab tiuxetan (Zevalin; Biogen Idec, Inc., Cambridge, MA, USA) and I-131 tositumomab (Bexxar; Corixa, Seattle, WA; and Glaxo Smith Kline; Philadelphia, PA, USA) have been associated with high response rates, durable remissions and limited toxicity apart from myelosuppression, making them ideal candidates for use in autotransplantation. Tested first as single agents in relapsed patients with indolent and transformed NHL, and then at much higher doses with stem cell support, these agents have now been combined with high-dose chemotherapy prior to autologous stem cell transplant. Radioimmunoconjugates have been used to replace total body irradiation (TBI) in some studies and to augment standard chemotherapy regimens in others. Thus far the results are promising, with combinations of radioimmunoconjugates and chemotherapy producing long-lasting responses in high-risk patients with no more toxicity than that caused by standard conditioning regimens. These results are notable in light of the fact that the dose of radiation delivered to the tumor is 10-fold higher than the dose achievable with TBI. Whether this increase in radiation dose to the targeted lymphoma translates into more durable remissions and an improvement in overall survival requires further investigation.