Breast adenocarcinoma can almost be thought of as an over-arching term for 'breast cancer'. An adenocarcinoma refers to a type of carcinoma that begins in glandular tissue (cells with a secretory function), such as the ducts and lobules of the breast. So, breast cancers which begin in the ducts or lobules are sometimes called adenocarcinomas, though the term can be applied to cancers of glandular tissue anywhere in the body.
Each breast typically has about 15 to 20 sections called 'lobes' and many smaller sections called 'lobules'.The lobules produce the milk, which is secreted into the ducts, and carried towards the nipple. Most breast cancers will start in either the breast ducts or the breast lobules, and because of the glandular tissue which comprises much of the ducts and lobues, these breast cancers are referred to as adenocarcinomas. The two main types of adenomacarcinoma are therefore infiltrating or invasive ductal carcinoma, and infiltrating or invasive lobular carcinoma. Lobular adenocarcinoma is actually much less common and tends to have a much better prognosis than ductal carcinoma. Invasive lobular carcinomas account for about 10-15% of breast cancers.
Around 80% of breast cancers are the infiltrating ductal carcinoma variety of adenocarcinoma, but there are also a number or rarer, specialized forms of adenocarcinoma, none of which account for more than 6% of breast cancers. Inflammatory breast cancer accounts for between 1% and 6% of breast carcinomas, while medullary breast carcinoma is estimated at 3%-5% of breast cancers. Mucinous breast carcinoma accounts for about 3%, tubular breast carcinoma for 1%-2%, and cribriform breast carcinoma for 5%-6%. Finally, there is papillary breast carcinoma which is estimated at between 1% to 2% of all breast cancers. (Some would include invasive lobular carcinoma within this specialized group). There are of course many other subtle variations and hybrid presentations of this core group of specialized adenocarcinomas.
Part of the histological evaluation of breast biopsy specimens usually involves the staining of a cytological sample for microscopic evidence of various proteins or hormones. Analysis of this staining process can help determine the feasibility of adjuvant chemotherapy, but prior to that, the process can greatly assist in the differential diagnosis of breast cancers. For examples, approximately 72% of breast adenocarcinomas over express the H19 gene as compared to healthy tissues. (Normal breast tissue does not express H19 RNA in the mammagry glands, except during puberty and pregnancy.) Hormonal receptors for estrogen (ER) and progesterone (PR), the Wilms tumor susceptibility gene 1 (WT1) and gross cystic disease fluid protein (GCDFP) are also useful for diagnosing breast adenocarcinomas.
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