The Absolute Monocyte Count Predicts Overall Survival In Patients Newly Diagnosed with Follicular Lymphoma

Follicular lymphoma (FL) is an indolent non-Hodgkin lymphoma (NHL) with a highly variable natural history. Clinical variables describing either patient- or tumor-specific characteristics, many of which are included in the Follicular Lymphoma International Prognostic Index (FLIPI), are used to risk-stratify patients at the time of diagnosis. However, characteristics of non-malignant cells present within the tumor microenvironment provide important prognostic information. For example, both immunohistochemistry and gene expression profiling studies demonstrate that lymphoma-associated macrophages (LAMs) are prognostically important in FL. As LAMs are monocyte-derived, we sought to determine whether the absolute monocyte count (AMC) obtained from a CBC at diagnosis is an adverse prognostic factor in FL.

Consecutive patients with FL who were evaluated and treated at the Mayo Clinic, Rochester between 1998 and 2007 were considered for study participation. Study approval was granted by the Mayo Clinic Institutional Review Board. The primary objective of the study was to determine the significance of the AMC, obtained at the time of diagnosis from a standard complete blood count with differential, in predicting overall survival. The secondary study objective was to determine whether the AMC is an independently significant prognostic factor when compared with the FLIPI.

The median follow-up was 4.2 years (range: 2 months to 11 years) for the 355 patients included in this study. At diagnosis, 43%, 34% and approximately 23% of patients were classified as low-, intermediate- or high-risk by the FLIPI. The median AMC at diagnosis was 510/μL, with 8% of patients presenting with an absolute monocytosis. At diagnosis, 45% of patients were initially observed, 42% received combination chemotherapy or immunochemotherapy alone, while the remaining 13% underwent surgery or radiation.

The AMC was evaluated as both a continuous and dichotomized variable on univariate analysis. The optimal cut-point for the AMC was determined to be 570/μL by ROC analysis and was used when analyzing the AMC as a dichotomized variable. A relative elevation in the AMC was associated with inferior overall survival, whether analyzed as a continuous or dichotomized variable, with hazard ratios (HR) of 1.002 (HR per unit change in AMC; 95% confidence interval 1.001–1.002; p=0.0002) and 3.4 (95% confidence interval 2.0–6.0; p<0.0001), respectively. The median OS for patients with an AMC <570/μL at diagnosis has not been reached, whereas a median OS of 10.2 years (95% confidence interval 7.8–11.2 years; p<0.0001) was observed for those patients with an AMC ≥570/μL. For comparison, median OS has not been reached for high-risk patients identified by the FLIPI. Among those patients who were initially observed, the median time to progression (TTP) was 31 months (95% confidence interval 25–37 months) for those with an AMC <570/μL at diagnosis. In contrast, patients with an AMC ≥570/μL experienced a significantly shorter TTP following initial observation, with a median TTP of 18 months (95% confidence interval 8–28 months; p=0.03). When adjusting for prognostic factors included in the FLIPI on multivariate analysis, the association between the AMC as a dichotomized variable and survival remained significant with a HR of 2.6 (95% confidence interval 1.5–4.6; p=0.001). When the FLIPI alone (high vs. low/intermediate) was analyzed on multivariate analysis, the AMC remained an independent predictor of survival (p<0.0001). Furthermore, the AMC provided additional prognostic information when superimposed upon the FLIPI. For example, a subset of patients classified as high-risk by the FLIPI were observed to have an OS comparable to low/intermediate risk patients identified by the FLIPI upon further risk-stratification by the AMC, with a 6-year OS of 80%. In contrast, high-risk FLIPI patients with an AMC ≥570/uL were observed to have a median OS of 4.2 years (95% confidence interval 2.7–7.2) and 6-year OS of 47%.

The AMC is associated with overall survival in FL and is independent from the FLIPI on multivariate analysis. While the AMC did not appear inferior to the FLIPI in identifying high-risk patients, it may be most helpful when used in conjunction with the FLIPI. These results further support the central role of nonneoplastic myeloid-lineage cells in FL biology.

No relevant conflicts of interest to declare.