IL2RG and neoplasm: However as few as 1/9 human melanoma cells were capable of initiating tumors when injected with growth factor rich matrigel into NOD/SCID Il2rg-/- mice.35 In summary, substantial studies suggest that not all tumor cells are capable of initiating or sustaining tumors, and the fraction, even within the same tumor, may vary, depending on the tumor microenvironment and changes in the microenvironment attendant with tumor growth or response to therapy.