Quantitative real-time polymerase chain reaction for monitoring minimal residual disease in patients with advanced indolent lymphomas treated with rituximab, fludarabine, mitoxantrone, and dexamethasone

Fludarabine and rituximab (Rituxan; Genentech, Inc, South San Francisco, CA, and IDEC Pharmaceuticals, San Diego, CA) are active against indolent lymphomas. We have previously shown the safety and efficacy of the combination of FND (fludarabine/mitoxantrone/dexamethasone) in relapsed and subsequently untreated patients with stage IV indolent lymphomas. Currently, we treat patients with stage IV indolent lymphomas who are previously untreated, younger than 60 years, human immunodeficiency virus-negative, and have adequate organ and marrow function with FND and random assignment to concurrent or delayed administration of rituximab. We have developed a quantitative real-time polymerase chain reaction assay for t(14; 18). With 1 μg of DNA, this assay detects 0.6 copies in 55% of reactions, as expected for the Poisson distribution. When 1 μg of DNA was analyzed in duplicate, cells with the t(14;18) were detected in peripheral blood of 22% of 152 volunteer blood donors. Quantitation showed that numbers of t(14;18) cells were higher than the statistical upper normal limit (mean of all volunteer values plus standard deviations) in 2% of volunteer blood donors. By contrast, 36% of blood or marrow specimens from follicular lymphoma patients were positive, and the number of cells with t(14;18) was higher than the normal upper limit in 26%. The presence of cells with t(14;18) and their numbers are prospectively quantitated in blood and marrow of patients treated with FND plus rituximab to determine their clinical significance both at presentation and during therapy.