Predictive factors for response to rituximab in Waldenstrom's macroglobulinemia.

Rituximab is an active agent for the treatment of Waldenstrom's macroglobulinemia. However, many patients do not respond to this agent and several others develop secondary resistance. In order to identify clinical and laboratory parameters that could predict a higher likelihood for response, we evaluated 54 patients who were treated with single-agent rituximab. Twenty-four patients (44%)exhibited > or = 50% reduction of serum monoclonal protein. Previously untreated and pretreated patients had the same probability for response. Low response rates were noted in patients with serum monoclonal protein level > or = 40 g/L (17%) and serum albumin level < 35 g/L (14%). Furthermore, a multivariate analysis indicated that high serum monoclonal protein and low albumin were the dominant variables associated with shorter time to progression. The presence of 2, 1, or none of these variables was associated with median times to progression of 4 months, 11 months, and approximately 48 months, respectively. We conclude that patients with low levels of monoclonal protein and normal albumin are the best candidates for treatment with rituximab.