Response assessment in chronic lymphocytic leukemia after fludarabine plus prednisone: Clinical, pathologic, immunophenotypic, and molecular analysis

The goals of this study were to evaluate the response to treatment in chronic lymphocytic leukemia (CLL) according to clinical, pathologic, immunophenotypic, and molecular features, as well as to address the clinical significance of each finding. One hundred fifty-nine CLL patients with either advanced Rai stage III or IV (81 patients) or progressive Rai stage 0 to II (78 patients) were treated with fludarabine (30 mg/m²/d intravenously every day for 5 days) plus prednisone (30 mg/m²/d orally daily for 5 days). Thirty-six patients were previously untreated. The response rates were 12% complete response (CR), 30% nodular complete response (nCR), and 18% partial response (PR). In all patients who achieved a complete response (both CR and nCR) less than 30% of nucleated cells were lymphocytes on marrow aspirate differential analysis; however, nCR patients had residual nodular and/or interstitial lymphocyte involvement on marrow biopsy examination. There was no evidence of leukemic infiltration on marrow biopsy examination in CR patients. With a median follow-up of 35 months, comparison of time to progression in the CR and nCR groups at 2 years showed a projected 87% versus 55% progression-free survival (P < .03). Residual disease assessment by flow cytometry using simultaneous dual-color staining on blood and marrow lymphocytes was also performed on each patient. Residual disease was determined by the expression of CD5 on B lymphocytes and the monoclonality of surface light-chain expression. After six courses of fludarabine plus prednisone, no residual disease was detected by flow cytometry in 89% of the CRs, 51% of the nCRs, and 19% of the PRs. Clinical residual disease in PR patients with no residual disease detectable by flow cytometry was limited to lymphadenopathy. Time to progression at 2 years was longer in CR and nCR patients having no residual disease detected by flow cytometry (84% v 39% 2-year progression-free survival, P < .001). Posttreatment Ig gene rearrangement analysis using JH, Jκ, and Cλ probes demonstrated no rearranged bands and a return to the germline configuration in five of seven CRs and two of eight nCRs studied. The molecular studies were concordant with the dual-parameter immunophenotype results and none of the patients who reverted to a germline DNA pattern after treatment have experienced relapse. The absence of detectable minimal residual disease by bone marrow biopsy, dual-color flow cytometry, and Ig gene rearrangement analysis is achieveable in CLL with fludarabine and is predictive of the response duration.