Pretreatment Patient Characteristics Associated with Achieving Bone Marrow Minimal Residual Disease-Free Status with Frontline Fludarabine, Cyclosphosphamide, Rituximab (FCR) Chemoimmunotherapy for CLL,

Abstract 3902

Chemoimmunotherapy (CIT) is highly effective treatment and standard of care for patients (pts) with CLL. Response to treatment by NCI-WG/IWCLL criteria correlates with outcome; pts who achieve complete remission (CR) have superior progression-free and overall survival compared to pts who achieve partial remission (PR); and pts who fail therapy have the poorest outcome. Emerging data indicate improved outcomes for pts who achieve minimal residual disease (MRD)-free status in blood or bone marrow (BM) by end of treatment. We are conducting a clinical trial to prospectively evaluate pretreatment pt characteristics and prognostic factors and correlations with NCI-WG response, MRD-free status, and time to event outcomes with standard frontline fludarabine, cyclophosphamide, and rituximab (FCR) CIT.

A total of 197 pts have been registered, 160 have completed treatment and are evaluable for response by NCI-WG criteria, and 127 have BM MRD status evaluated by standard 4-color flow cytometry at Course 3 and/or end of treatment. We report on pretreatment characteristics associated with MRD-free status at end of treatment. For the 160 pts evaluable for response by NCI-WG criteria, 63% were male; the median (range) age, β2M, and absolute lymphocyte count (ALC) were 58 yrs (38–84), 3.6 mg/l (1.3–14.1), and 78.7 K/μl (.8–394), respectively. The percent pts with Rai high-risk disease, unmutated IGHV status, ZAP70⁺ by immunohistochemistry (IHC) and CD38⁺ (30% cutoff) was 35%, 60%, 63%, and 37%, respectively. According to the hierarchical categorization, FISH demonstrated 17p del in 9%, 11q del in 18%, +12 in 17%, 13q del in 36%, and no abnormality in 20% of pts. The median number of FCR courses given was 6; 57% received all intended 6, 21% received 4–5, and 23% received ≤3. Of the 160 pts, 63% achieved CR, 12% nodular PR (nPR), 23% PR and 3% did not respond. Of 127 pts with BM evaluated by 4-color flow cytometry at end of treatment, 56% were MRD-free. Of 71 MRD-free pts, 27 were negative at end of course 3, 33 converted to negative after course 3, and 11 were negative at end of treatment but did not have a course 3 evaluation. Univariable Chi-square analyses demonstrated pretreatment β2M, IGHV mutation status, 17p del, and +12 correlated with MRD-free status at end of treatment (Table). The following did not correlate: age, Rai stage, WBC, ALC, HGB, PLT, ZAP70, CD38, or number of FCR courses received. Multivariable logistic regression model identified β2M≥4 mg/l (odds ratio=.78; p=.007) and unmutated IGHV (odds ratio=.77; p=.006) as independently associated with lower likelihood to achieve MRD-free status.

In conclusion, mutated IGHV and β2M <4 mg/l are independently associated with increased likelihood of achieving MRD-free status with frontline FCR CIT; further follow up is needed to correlate MRD-free status with improved survival outcomes for patients treated on this trial.