Functional iron-deficiency anemia (FIDA) is a side effect of many cancer treatments, occurring when chemotherapy drugs damage bone marrow cells, which are responsible for producing red blood cells, due to the myelosuppressive effects of chemotherapy, or to the cancer itself. This study was performed to compare the effects of darbepoetin alfa alone, or in combination with ferric derisomaltose in cancer patients with FIDA, and to elucidate the mechanism underlying the effects in F36E cells. F36E cells treated with darbepoetin alfa showed increased cell viability. AML and GC cells treated with darbepoetin alfa, ferric derisomaltose, or ferric derisomaltose plus darbepoetin alfa showed no induction of apoptosis. The effects of these drugs on the anticancer efficacy of PTX chemotherapy were examined by analyzing cell viability and induction of apoptosis. Darbepoetin alfa, ferric derisomaltose, and ferric derisomaltose plus darbepoetin alfa showed no significant inhibitory effects on the apoptosis-inducing activity of PTX in GC cell lines. Patients with chemotherapy-induced FIDA in Group I receiving ferric derisomaltose plus darbepoetin alfa showed higher hemoglobin levels, transferrin saturation, and ferritin levels compared to those in Group II, treated with darbepoetin alfa alone. In cancer patients with FIDA, the prognosis of anemia treatment was better in the ferric derisomaltose plus darbepoetin alfa combination group than in the group receiving darbepoetin alfa monotherapy.