Monocyte nadir is a possible indicator for neutrophil nadir during lung cancer chemotherapy

INTRODUCTION: No previous study clearly demonstrated the association between the absolute neutrophil count (ANC) nadir and the absolute monocyte count (AMC) nadir among patients undergoing chemotherapy. METHODS: We retrospectively reviewed patients with an incurable lung cancer in two university hospital who were treated with platinum doublet or triplet. In this study, the nadir was defined as the lowest value during days 1-22. RESULTS: We observed 75 patients: 61 men (81%) and 14 women (19%), median age of 69 years. The number of days that elapsed between the first day of chemotherapy and the median ANC nadir of 12 days was longer than that for AMC nadir of 6 (Wilcoxon signed rank test: P < 0.001). The number of days that elapsed between the first day of chemotherapy and the AMC nadir was the only factor that had a significant correlation with that for ANC nadir (Spearman's rank correlation: r = 0.34, P = 0.003). Among 75 patients, 23 (31%) had an ANC at nadir <1000/μL. AMC at nadir of 100/μL predicted an ANC at nadir <1000/μL with a sensitivity of 83% and a specificity of 56%. CONCLUSION: Both neutrophils and monocytes are differentiated from a common progenitor, a granulocyte macrophage colony forming cell, which can provide good explanation for the association between ANC and AMC nadirs. We would like to recommend physicians to observe the AMC nadir to predict the timing and severity of the ANC nadir.