The majority of breast cancers arise from which part of the breast anatomy?

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The main concept is that most breast cancers originate in the terminal ductal-lobular units, which are the functional units at the end of the ductal system where ducts meet tiny lobules that produce milk. These units line the epithelium with ductal and acinar (lobular) cells, and it’s in this epithelial layer that genetic mutations commonly accumulate, leading to malignant transformation. Because the majority of the breast’s epithelium—and therefore its cancer-prone tissue—resides in the terminal ductal-lobular units, this region is the typical origin for cancers. The stroma is the connective tissue framework and is less often the source of epithelial cancers. Lobules are part of the terminal ductal-lobular unit, so cancers arising in the lobular component are still within this broader site.