Objective: To investigate the effect of dietary protein quality on ovarian cancer growth and its synergism with an anticancer drug, using murine ovarian cancer models.

Method: We first established four groups of mice, which were fed 20% or 10% animal protein or plant protein, respectively. We injected an ovarian cancer cell line (HM-1) subcutaneously and intraperitoneally into immunocompetent B6C3F1 mice and examined the tumor size and body weight of the mice over time. We also injected cisplatin into the mice intraperitoneally and observed tumor size, body weight and survival. Different rates of tumor growth were confirmed by immunohistochemistry in the mice using Ki-67 index.

Results: The inhibition of tumor growth of the subcutaneously implanted cancers were observed in order in the mice fed with 20% plant, 10% plant, 10% animal and 20% animal protein diet (p<0.0001).  After the injection of cisplatin, the tumor size in the mice fed with 20% plant protein diet showed a significant decrease in comparison to the mice fed with 20% animal protein diet (p<0.0001). The proliferation index (Ki67 index) was higher in the mice that were fed animal protein diet. Furthermore, the body weight in the mice that were fed 20% animal protein diet without tumor injection was significantly decreased by cisplatin treatment in comparison to those that were fed 20% plant protein diet (p<0.0001). The survival of the mice fed 20% animal protein diet was worse than the mice fed 20% plant protein diet (log-rank test, p=0.0007).

Conclusions: Our findings suggest that replacement of dietary animal protein with plant protein could be effective in inhibiting tumor growth and might reinforce an anticancer drug’s effect synergistically, and could result in a better prognosis in ovarian cancer.