It has been demonstrated that increased RNase1 expression in serum or plasma of cancer patients is mainly sourced from tumor cells.[6, 11] To test whether RNase1‐overexpressing 4T1 tumor possesses a supraphysiological level of RNase1 in serum of mice, BALB/c mice were implanted with 4T1‐pCDH, R1, sh‐Ctrl, and sh‐mR1#1 cells and mouse serum were collected after tumor inoculation for 20 d. This evidence concerns the gene RNASE1 and cancer.