the primary breast. Instead, there is a growing awareness that separate focal vestigial breast mounds are consistently present in adults, located in pairs running down the curved lines of the embryological mammary ridges. It may be of great oncologic and surgical benefit if breast cancer formation and metastasis were reinterpreted in light of this new anatomic understanding. For example, it appears that the axillary mound is more likely to contain accessory ductal tissue than any of the other accessory fatty mounds along each mammary chain, perhaps more commonly serving as a nidus for breast cancer formation, though incidence of tumor formation in the other vestigial breast mounds has not been established. Breast cancer Breast cancer can develop in the tail of Spence. One form is referred to as carcinoma of the axillary tail of Spence (CATS). Various studies have calculated CATS as representing 0.1-1% of breast cancers. These cancers may actually represent de novo tumors forming in the anatomically separate axillary breast mounds that were previously thought to be tail-like extensions of the primary breast. See also Anatomical terms of location Breast cancer Human anatomy Mammary ridge References Breast anatomy