Persistently low lymphocyte counts after FCR therapy for chronic lymphocytic leukemia are associated with longer overall survival.

Decreased absolute lymphocyte counts (ALCs) following frontline therapy for chronic lymphocytic leukemia may be associated with disease control, even in patients without evidence of minimal residual disease. We studied the prognostic significance of ALCs during the first year following treatment with fludarabine, cyclophosphamide, and rituximab (FCR). We evaluated 99 patients who achieved a partial response without lymphocytosis (<4.0 × 103 cells/µL) or better after FCR. Absolute lymphocyte counts were recorded at 3-, 6-, 9-, and 12-month posttreatment and correlated with overall survival (OS) and event-free survival (EFS). For each time point, analyses were limited to patients without lymphocytosis, so as to avoid possible biases from undocumented disease progressions. Lymphopenia (ALC < 1.0 × 103 cells/µL) at 3 m after FCR (69% of patients n = 68), was associated with a longer OS (5y OS 91% vs 64%, P = .001), as were ALC ≤ 2 × 103 cells/µL at 6 m (5y OS 85% vs 48%, P = .004) and ALC ≤ 1.8 × 103 cells/µL at 9 m (5y OS 93% vs 54%, P = .009). A normal-range ALC (≤4 × 103 cells/µL) at 12 m was also associated with a 91% 5y OS. Higher ALCs (but without lymphocytosis) were associated with shorter EFS (median EFS 27 months for ALC > 1.8 vs not reached for ALC ≤ 0.7 at 9 months, P < .0001). In conclusion, lower ALC levels in the first few months following frontline FCR therapy were associated with longer OS and EFS. Possible explanations may be that lower ALCs reflect deeper clonal suppression or protracted Treg depletion. Absolute lymphocyte count levels may be a cheap and widely available prognostic marker, though the added value for clinical practice is the minimal residual disease era needs to be explored.