IL21 and malignant colon neoplasm: Thus, we can speculate the following: 1) VVLΔTKΔN1L has a poor therapeutic effect and affinity for colon cancer; 2) C57BL/6 mice and BALB/c mice have different genetic backgrounds and immune responses to the virus; 3) IL-21 may mediate antiviral immunity and lead to virus clearance; and 4) tumor heterogeneity is an essential factor affecting the efficacy of treatment.