There are several different kinds of invasive breast cancer, as well as tiny noninvasive carcinomas in situ, which may or may not progress to an invasive stage. As in other types of cancer, breast cancer is now classified both by the general type and, more specifically, by cell type. Cell classification is important because the different types grow and metastasize at varying rates; therefore the more a doctor knows about the type of cancer, the easier it is to develop an effective treatment regimen.
Specific types of breast cancer are:
- Invasive ductal cancer. About 70 percent of all breast cancer falls into this category. The cancer cells themself lack specific distinguishing characteristics. The cancers are hard to the touch and, in advanced stages, may cause visible dimpling of the skin or retraction of the nipple. This type of cancer tends to spread rather rapidly to the lymph nodes, even while it is still quite small, and it carries a poorer prognosis than some other types.
- Medullary carcinoma. This type of ductal cancer accounts for about 7 percent of breast cancer. It is distinguished by its appearance: it seems to grow in a capsule within the duct and although it may become quite large, it does not metastasize as frequently as the more common invasive ductal cancer and has a better outlook.
- Comedocarcinomas. These make up about 5 percent of breast cancer. The tumor begins in the lining of the duct, and grows into the duct itself until it is completely filled. The ducts become dilated to accommodate the larger amount of material in it. When removed and examined in a cut section, the ducts resemble blackheads, hence the name comedocarci-noma. The tumor can grow quite large, but it is not as likely to spread beyond the breast or invade the skin as some other forms of breast cancer; therefore the prognosis is generally good.
- Mudnous carcinoma. This is still another form of ductal cancer, so named because its cells produce mucus. It accounts for about 3 percent of breast cancer, and like comedocarcinomas, it may grow quite large without metastasizing.
- Tubular ductal cancer. This relatively rare form—it accounts for about 2 percent of all breast cancer—derives its name from the tumor structure. When viewed under the microscope, the tumor shows tube-shaped structures ringed with a single layer of cells. The outlook is better than for invasive ductal cancer.
- Invasive lobular carcinoma. These cancers, which account for about 3 percent of breast cancer, start in the breast lobules—the small end ducts that branch off the lobes. The cancer is similar to the invasive ductal type and, like it, has a generally poor outlook.
- Lobular and ductal carcinomas in situ. These are tiny cancers that are confined to either the lobules or ducts. They are too small to be felt, but they sometimes appear as tiny areas of calcifications on a mammogram. Often they are discovered during a biopsy for another larger breast lump. A breast will frequently contain several in situ cancers; some of these eventually develop into invasive cancers, and it is impossible to tell which lesions will become invasive and which will not. Thus there is disagreement among specialists as to how these in situ carcinomas should be treated. It is very rare for carcinomas in situ to spread to the lymph nodes; therefore some doctors advocate a wait-and-see approach, with regular mammography and regular breast examinations to detect any change in an early stage. Others advocate a curative mastectomy, especially if there are other risk factors such as a family history of breast cancer early in life.