Breast cancer is the most commonly diagnosed malignancy among women in the US. Epidemiology shows that a high animal fat diet increases risk of triple-negative breast cancer (TNBC). Our previous work examined the effect of pre-pubertal exposure to high dietary animal fat in the SV40Tag mouse model of TNBC. We showed that a high animal fat diet changes mammary fat composition and increases incidence and aggressiveness of mammary cancers in this model. Here, we demonstrate using MR angiography that changes in fat composition and cancer incidence are paralleled by increases in vascular density in the mammary gland.