I am very pleased that your bone marrow test following cladribine shows no evidence of hairy cell leukemia. You indicate that you are concerned that you "probably have minimal residual disease (MRD) that could cause a return of the hairy cell leukemia in the future." The doctor can use special laboratory tests to evaluate the possible extent of minimal residual disease (MRD) in your remission bone marrow sample. However, these evaluations for MRD are being done on patients who are participating in clinical trials so that we will be able to evaluate the accuracy of using this information in the future to predict who will relapse and require therapy. You are correct that there is a possibility that you do have MRD following cladribine, but there are no studies absolutely confirming when and if treatment should be given to eradicate this minimal disease.

As you know, there have been a few reports that indicate that MRD after initial successful treatment with cladribine or pentostatin can be eradicated by Rituximab. Although this appears to be reasonable, there are few data to show that this has a positive effect on preventing relapse and providing an ultimate survival benefit. Some reports have suggested that the use of Rituximab might be better utilized after the initial relapse has occurred.

There are other unanswered questions. What is the optimal time to use Rituximab? What is the best dose and schedule for giving this therapy? For example, should the treatments be given weekly for four or eight weeks? Should Rituximab be given along with the original cladribine? Or should it be given after cladribine? Finally, should its use be reserved for after the initiation of therapy for definite relapse?

While the demonstration of MRD by extensive testing on the patient's bone marrow sample may ultimately be the best practice following treatment with cladribine, the demonstration that there is MRD is not a definite indication to re-start more therapy. If the patient's blood counts have normalized, it might be very reasonable to follow the patient with MRD until there is an indication to re-treat the leukemia. If the patient has no symptoms and relatively normal blood counts, careful follow-up might be the best approach. It is important for patients to be encouraged to participate in organized clinical trials to help address these important questions.