The working machinery of the breast consists of lobules, the glands where milk is made, and ducts, the passageways through which the milk passes on its way to the nipples. The breast also contains fatty tissue, ligaments that support the ducts and lobules, blood vessels, and lymphatic vessels. Lymphatic vessels are similar to veins, except that they carry lymph instead of blood. Lymph is a clear fluid containing the waste products of tissues and large numbers of white blood cells that fight infection. Cancer cells can enter the lymph vessels. Most of the lymphatic vessels of the breast lead to lymph nodes in the armpits.
Cancer can occur either in the ducts or the lobules, but ductal cancer is the most common and worrisome kind. Fortunately, with better technology and more accurate mammograms, we are finding ductal cancer earlier than we did in the past.
How does breast cancer develop?
Like other cancers, breast cancer develops through a series of gradual changes, which progress from normal breast tissue to full-fledged cancer. The first step is proliferative fibrocystic disease, also called hyperplasia (a word that simply means “overgrowth”). This condition is not cancerous: the cells divide faster than normal cells, but are otherwise normal.
The next stage is called atypical hyperplasia. The cells are growing and dividing abnormally fast (hyperplasia), and some of the fast-growing cells have unusual characteristics (atypia). The presence of hyperplasia with atypia is an early warning that the breast is at increased risk for developing cancer, but it is not in itself cancer. Women who have this condition are about four times as likely to get breast cancer as women who do not; they should be extremely vigilant about breast exams and have more frequent mammograms than women less at risk. But most of the time, women with atypical hyperplasia can live normal lives without overwhelming anxiety.
The next development is carcinoma in situ. Cancerous changes occur within some of the cells of the breast, but these abnormal cells do not invade their neighbors. In the next stage, invasive carcinoma, the abnormal cells invade nearby tissue and may also infiltrate blood vessels or lymph nodes. The sequence of changes, from normal to cancerous, is the same whether the cancer is in the ducts or in the lobules, though the prognosis is different.
A carcinoma is a cancer that begins in the lining layer (epithelial cells) of organs. At least 80 percent of all cancers and almost all breast cancers are carcinomas. Ductal cancer is the development of malignant cells within the ducts that carry milk.
Another name for ductal carcinoma in situ, sometimes abbreviated DCIS (in which the cancerous changes remain confined to the ductal cells), is intraductal carcinoma. It has a very good prognosis: if the cancer is removed, the disease is cured. If the cancer has become invasive, the prognosis is more difficult.
Lobular carcinoma, which develops in the lobules where milk is produced, has the same two stages as ductal carcinoma: either it is confined to the lobule itself — in situ lobular carcinoma — or it has spread to adjacent blood vessels or tissue and become invasive.
If an in situ lobular carcinoma is removed, the disease is cured and no further cancer treatment is necessary. However, women who have had in situ lobular carcinoma are at about 33 percent increased risk for developing breast cancer, either in the breast that was previously involved or in the other one. Lobular carcinoma that has invaded nearby cells, blood vessels, or lymph nodes must be treated more aggressively.
Inflammatory carcinoma, the third kind of breast cancer, originates in the lymphatics within the underlying layer of the skin and is quite rare, accounting for only about 1 percent of breast cancers. Inflammatory carcinoma looks like a hot, red area on the skin of the breast. Often the skin looks textured or pitted, like the skin of an orange; sometimes the breast develops ridges and small bumps that look like hives. These symptoms are caused by cancer cells blocking lymph vessels in the skin over the breast.