Table 2 Invasion grading of subcutaneous xenograft tumor in the footpad [28]

Grade 0

Tumor cells begin to proliferate at the inoculation site. The tumor margin is neat and tumor cells do not invade surrounding tissues

Grade I

There is mild edema around the tumor tissue and a small number of inflammatory cells infiltrated. A single tumor cell begins to invade surrounding tissues and host tissues do not change

Grade II

The growth of tumor cells is active and surrounding tissues have evident edema. A large number of inflammatory cells surround the tumor body. Groups of tumor cells invade muscle tissues, but degeneration and atrophy are not observed

Grade III

Tumor cells invade muscle tissues diffusely and muscle cells appear degeneration and atrophy. The edema and inflammation around the tumor are more evident. The center of the tumor appears necrosis. Meanwhile, tumor cells have invaded the dermis, but atrophy or thinning is not observed in the epidermis

Grade IV

Tumor cells invade subcutaneous tissues diffusely and some invade the epidermis, making the epidermis thinner or broken. Most of the muscle tissues and some bone tissues are invaded, and there is extensive necrosis in the center of the tumor