Sticking to maintenance therapy after remission reduces relapse risk in childhood ALL

This study examined the effect of adherence to maintenance therapy on relapse risk in Hispanic and non-Hispanic children with acute lymphoblastic leukemia (ALL). Researchers concluded that lower adherence to maintenance therapy increases relapse risk. Ethnic differences in relapse risk differed depending on the level of adherence.

ALL is a cancer of the blood and bone marrow. It is the most common type of childhood cancer. While remission (no sign of disease) is often reached in children after primary treatment, it has been estimated that about 20% relapse within 5 years. Factors such as age at diagnosis and ethnicity can affect relapse risk. ALL in Hispanic children is often associated with poorer outcomes. In order to maintain remission and reduce the risk of relapse, maintenance therapy with the chemotherapy drug mercaptopurine (Purinethol) is recommended for 2 years after primary treatment. 

The aim of this study was to examine the effect of adherence to maintenance therapy on relapse risk in Hispanic and non-Hispanic children with ALL.

327 children with ALL were included in this study. Of these, 169 were Hispanic and 158 were non-Hispanic white. All children were in their first remission after primary treatment and on maintenance therapy with mercaptopurine. Treatment adherence to mercaptopurine was measured for 6 months using an electronic monitoring device on the medication bottle. Patients were followed for an average of 3.7 years.

Treatment adherence significantly declined from 94.7% (at Month 1) to 90.2% (at Month 6). Average adherence over 6 months was significantly lower among Hispanics (88.4%) compared to non-Hispanics (94.8%). Adherence was lower when patients were aged 12 years or older (85.8%) compared to patients younger than 12 years (93.1%). Adherence was also significantly lower among patients in single-mother households (80.6%).

Lower adherence significantly increased the risk of relapse. The risk increased about 4-fold if adherence was between 85% and 94.9% (when compared to an adherence of 95% or higher). Relapse risk was 5.7 times higher if adherence was below 85%.

The relapse rate at 4 years was 16.5% for Hispanic patients. This was significantly higher compared to non-Hispanic whites (6.3%). Overall, relapse risk was 2.6 times higher for Hispanic patients. However, after accounting for treatment adherence to mercaptopurine and socioeconomic status, this was no longer statistically significant. At adherence rates of 90% or above, Hispanics continued to show higher relapse. At adherence rates below 90%, relapse risk was comparable among the two ethnicities studied.

Researchers concluded that lower adherence to maintenance therapy increases relapse risk in children with ALL. Hispanic patients were at increased risk of relapse, however, only at higher adherence rates.