PurposeThe evaluation of regulatory T (Treg) (CD4+CD25high CD127neg) lymphocyte count with respect to the T helper (TH) (CD4) number has been shown to represent the main immune parameters capable of signifying the functional status of the anticancer immunity in cancer patients. This study is aimed to explore a correlation between therapy efficacy and changes in Treg/TH ratio and other biochemical and haematological parameters in patients with metastatic colorectal cancer (mCRC).Experimental DesignMeasurements of regulatory T cells were performed by flow cytometric analysis pre- and post-therapies in a prospective study.ResultsWe investigated levels of Treg/TH ratio in the peripheral blood of 25 mCRC patients pre- and post-chemotherapy ± targeted therapy. There were significant differences in levels of Treg/TH ratio pre- and post-treatments among patients on study, patients with partial response (PR), stable disease (SD) and progressive disease (PD) (P= 0.012, P= 0.011, and P= 0.043, respectively). Moreover, the relative change in Treg/TH ratio showed statistically significant difference among patients with PD as compared to those with PR and SD. Our findings demonstrated a statistically significant strong correlation between the relative change in Treg/TH ratio and therapeutic response. (Spearman's rho= 0.788/p<0.001).ConclusionsThe monitoring of the relative change in Treg/TH ratio could constitute a promising clinical index for response prediction and a timely change in regimen. Further prospective evaluations of these parameters investigated, particularly their association with overall survival, are warranted.