Leslie Andritsos, MD: Both purine nucleoside analogs, cladribine and pentostatin, result in very high complete response [CR] rates. Patients will typically start to demonstrate hematologic responses relatively early in their treatment course, usually within the first month of treatment. And so the neutropenia that is sometimes seen, either as a baseline feature of the disease or as a result of treatment, will usually start to resolve relatively early in the treatment cycle. That helps with alleviating the risk of bacterial infections.

However, these drugs are very immunocompromising, and patients may still be at risk of viral infections or opportunistic infections. So we typically will provide antimicrobial prophylaxis, especially for HSV [herpes simplex virus], VZV [varicella zoster virus], and PJP [pneumocystis jirovecii pneumonia]. Once patients have finished their therapy, it is important to repeat a bone marrow biopsy to demonstrate the depth of their response. Even patients who achieve a complete hematological response may have a significant amount of disease in their bone marrow at the completion of therapy. It’s hard to know what their prognosis is going to be without doing that bone marrow biopsy.

For most of our patients, we recommend a repeat bone marrow biopsy about four months after finishing cladribine, and a repeat bone marrow biopsy after completion of pentostatin, which takes about six months. So we perform end of treatment sampling to see if patients have achieved a CR. We know that the patients who do achieve a CR tend to stay in remission longer than patients who have measurable residual disease, especially if there’s more than 5% hairy cell leukemia in the bone marrow at the end of treatment. Patients who are in remission may still be at risk of infection, even with normal blood counts. And so we typically will see these people about every three months for routine laboratory monitoring, infection monitoring, and with strict instructions to call if they develop a fever or symptoms of infection.

Gary J. Schiller, MD: To me, the most important thing for community oncologists who are treating hairy cell leukemia is to recognize the potential risks of highly active drugs. In the case of purine nucleoside drugs, late opportunistic infection, viral reactivation, and pneumocystis pneumonia are of such a frequency that prophylactic antibiotics really need to be given with even a one-week therapy with a purine nucleoside analog. The community oncologist has a lot of experience already with rituximab, so, in the second-line setting, I think that they’re very much capable of handling the potential toxicities. But again, a patient whose relapse is relatively early, within one to two years after initial therapy; or a patient who’s had multiple relapses; or a patient whose disease is characterized by unusual features, such as extreme lymphocytosis, that kind of patient is probably better served in a specialty clinic that has access to investigational drugs and has experience perhaps in combining drugs that hit multiple targets.

Transcript Edited for Clarity