Limitations of a murine transgenic breast cancer model for studies of erythropoietin-induced tumor progression.

Adverse effects of erythropoietin (EPO) on tumor progression and survival were observed in recent phase 3 oncology trials. However, mechanisms remain poorly understood. We tested the effects of exogenous EPO on murine B16F10 melanoma growth in a subcutaneous tumor transplant model, and for the first time, in a model of spontaneous tumor formation within autochthonous epithelial tissues using murine mammary tumor virus promoter polyoma virus middle T antigen (MMTV-PyMT) transgenic mice. EPO receptor (EPOR) messenger RNA (mRNA) was detectable in both B16F10 tumors and mammary tumors from MMTV-PyMT mice but was 0.12 +/- 0.02% and 1.3 +/- 0.91% of the EPOR mRNA level in murine erythroid HCD-57 cells, respectively. B16F10 tumor growth rates in mice treated for 3 weeks with 30 microg/kg per week of darbepoetin alpha, 0.41 inverse days (range, 0.05-0.69 inverse days; n = 16), were similar to tumor growth rates observed in mice treated with PBS, 0.42 inverse days (range, 0.10-0.69 inverse days; n = 17). In contrast, darbepoetin alpha raised hematocrit levels to 0.593 (maximum, 0.729) compared with 0.448 (maximum, 0.532) in PBS-treated mice (P = .0004). In MMTV-PyMT mice, the weights of tumor-bearing mammary glands in mice treated for 6 weeks with 30 microg/kg per week of darbepoetin alpha, 3.37 g (range, 1.94-5.81 g; n = 27), did not significantly differ from the weights in PBS-treated mice, 3.76 g (range, 2.30-6.33 g; n = 26). In contrast, darbepoetin alpha raised hematocrit levels to 0.441 (maximum, 0.606) compared with 0.405 (maximum, 0.492) in PBS-treated mice (P = .05). Thus, effects of exogenous EPO on tumor growth were not recapitulated in these murine tumor models.