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What Is Breast Cancer?

By , Caring.com senior editor
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If you're caring for someone who's been diagnosed with breast cancer, it's helpful for you to get grounded in the basics of the disease. Breast cancer usually starts with a cancerous, or malignant, tumor located in the breast tissue. Most breast cancers are located in the area around the nipple. For women, breast cancer is the most common cancer and the second leading cause of cancer deaths, following only lung cancer. Although men can get breast cancer, it's rare (only one half of 1 percent of all breast cancers are in men).

How breast cancer is discovered

Most breast cancers are found when a woman feels a lump or hard area within her breast or when a suspicious area turns up on a mammogram. Not all tumors are malignant; doctors determine whether one is by taking a biopsy of the tumor tissue. Then they can examine whether cells are growing in the out-of-control fashion that indicates cancer.

The majority of breast tumors are described as being either lobular or ductal. These terms refer to the location of the tumor: whether it's located in a lobule, or milk-producing gland, or in a duct, one of the tubes connecting the lobules with the nipple.

In situ and invasive breast cancer

One of the first things doctors try to establish is whether a breast tumor is contained within its original location or has spread to surrounding tissue. To determine this, doctors use two terms:

  • In situ. This means the malignant cells are contained within the original area -- that is, within the duct or lobule. Women with very early-stage breast cancer will be told they have ductal carcinoma in situ or lobular carcinoma in situ. These are also sometimes called stage 0 because they aren't invasive.
  • Invasive (or infiltrating). This means the cancerous cells have broken through the wall of the duct or lobule and are expanding into other areas. The most common type of breast cancer is invasive (or infiltrating) ductal carcinoma (IDC), which means cancer that started within a milk duct has now spread into the fatty tissue of the breast. Eight in ten of all breast cancers are IDC. Invasive lobular carcinoma, or ILC, is much less common, accounting for only one in ten invasive breast tumors.

The rarest type: Inflammatory breast cancer

Inflammatory breast cancer, a form of invasive breast cancer, accounts for only 1 to 3 percent of all breast cancers. This type of cancer doesn't start with a lump or tumor. Instead, it begins by blocking lymph vessels in the skin. Women with inflammatory breast cancer may notice their breasts are red, swollen, and painful, and the skin may have a thick, pitted appearance that's often described as resembling orange peel. Unfortunately, inflammatory breast cancer is often mistaken for mastitis, or infection of the milk ducts around the nipple.