Understanding Relapse of Hairy Cell Leukemia

Patients who are treated for hairy cell leukemia should have a bone marrow biopsy performed following treatment to determine if a complete response (eradication of all evidence of hairy cell leukemia) has been achieved. Among patients who have achieved a complete response, it is not unusual to find minimal residual disease (MRD) if more sophisticated studies are done to detect a small amount of hairy cells not visible under the regular microscope. Minimal residual disease may be one reason that some patients ultimately relapse.

Patients are usually followed quarterly after they have completed therapy. Routine blood counts are obtained to ensure that the remission is being maintained. If blood counts show a decline, a repeat bone marrow may be obtained to see if the disease is relapsing by identifying a small amount of recurrent hairy cells. Immunophenotyping studies (looking for certain markers on the surface of the lymphocytes to identify hairy cells) may be done to look for a small amount of recurrent hairy cells.

If relapse has been documented, careful consideration is given to decide if and when to re-initiate treatment. Just as there is a watchful waiting approach at the time of initial diagnosis, a similar strategy may be followed in patients who have a small amount of recurrent hairy cells, but are without symptoms. A small decline in the blood counts may not be sufficient to warrant re-treatment since often this disease is slow-growing. However, there is an advantage to re-starting therapy before the counts deteriorate to very low dangerous levels.