Prognostic Significance of Quantitative t(14;18) PCR Monitoring in Advanced Stage Follicular Lymphoma Patients.

In a prospective multicenter phase III trial (M 39023) advanced stage follicular lymphoma (FL) patients were randomized to receive eight cycles of MCP (mitoxantrone, chlorambucil, prednisolone) chemotherapy alone or in combination with rituximab (R-MCP). This study was carried out to determine the effects of this therapy on circulating lymphoma cells (CLC) and to assess the value of CLC quantitation as a molecular marker of disease activity and as a prognostic parameter. CLC numbers were determined by real-time quantitative PCR for the t(14;18)-MBR translocation or by allele-specific PCR for rearranged immunoglobulin heavy chain genes. Quantitative PCR of a reference gene (wild type K-ras) allowed the exact quantitation of cells tested per sample and to exclude samples with insufficient DNA content (< 500,000 cells). We analyzed serial blood samples from 43 patients obtained before, during and after completion of therapy. Baseline clinical characteristics and response to therapy of the 43 patients of this study were not significantly different to all 201 FL patients of the clinical trial except for a higher complete response (CR) rate in the R-MCP group (18/25 (72%) in this study versus 52/105 (50%) in the clinical trial, p=.04). Similar to the results of the clinical study, response rate and CR rate in the present study were significantly higher in the R-MCP arm than after therapy with MCP alone (25/25 (100%) versus 13/18 (72%), p= .009, and 18/25 (72%) versus 5/18 (28%), p= .006, respectively). Clearance of CLC at the end of therapy was achieved in 21/25 patients (84%) treated with R-MCP compared to 0/18 (0%) after MCP alone (p< .0001). R-MCP patients achieved a greater reduction of CLC after completion of therapy and a greater reduction of CLC per treatment cycle than patients treated with MCP alone, even if the comparison was restricted to patients with clinical response (3.88 log and 1.18 log reduction versus 2.21 log and 0.23 log reduction, p= .001 and p< .0001). A ≥ 2 log reduction of CLC after completion of therapy was associated with a favourable clinical response (p= 0.0007) and prolonged event-free survival (p= 0.02) regardless of treatment arm. Among patients with a ≥2 log CLC reduction there was no significant difference in EFS between patients with PCR negative samples and patients with PCR positive blood samples at completion of therapy (p= 0.091). In conclusion, R-MCP led to a rapid and sustained eradication of CLC in the majority of patients. The results of serial determinations of CLC numbers showed a good correlation with the quality and duration of the clinical response. Therefore, quantitative molecular disease monitoring could help to develop individualized treatment strategies for patients with advanced stage FL.