The objective of this study was to evaluate the determinants and clinical significance of blood hemoglobin (Hb) levels, erythrocyte MCV levels, and different anemia subgroups in two independent prospectively recruited successive cohorts of 148 CRC patients (Cohort 1) and 208 CRC patients (Cohort 2), with special emphasis on the relationships between blood Hb and the systemic inflammatory response. This evidence concerns the gene GSTM1 and anemia (phenotype).