Our findings were also confirmed by a multicenter retrospective study evaluating the comparative effectiveness of biosimilar of epoetin alfa vs. darbepoetin alfa after about four weeks of treatment in cancer patients from a community-based single German center (mean baseline Hb value (g/dL): biosimilar: 9.8; darbepoetin alfa: 9.9; mean Hb at end of ESA treatment (g/dL): biosimilar: 11.9; darbepoetin alfa: 11.9). Here, GSTM1 is linked to cancer.