Fig. 3.

Intradermal B16 melanoma tumors in young mice show features of aggressive, rapidly growing cells compared to tumors in old mice. (A) Aggressive behavior in 8-month-old CB6 F1 mice is seen as vertical growth and invasive spreading with irregular nodular contour and irregular infiltrating cells within the epidermal and dermal layers (40× and 200× power). (B) Intradermal tumors in 32-month-old CB6 F1 mice showed a radial growth pattern with superficial spreading of tumor cells in a well demarcated nodular contour (40× and 200× power).