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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.

The importance of lymph nodes: Has the cancer spread?

The lymphatic system carries fluid that fights infection, and the lymph nodes and vessels near the breast and under the arm are one of the first places breast cancer typically spreads. Once in the lymph nodes and vessels, cancerous cells can be carried to other areas of the body.

Doctors biopsy lymph nodes to assess if breast cancer has spread. You'll hear the term lymph node involvement as a marker for whether a cancer is contained within the breast or is metastatic , which means it's spreading to other areas. The term sentinel node refers to the lymph node that doctors determine is the first node into which a tumor might drain; this node is usually biopsied.

Breast cancer tests for diagnosis and staging

Once a mammogram, ultrasound, or MRI locates a potential tumor, the doctor may order additional tests to see if the cancer has spread:

  • Blood tests can assess kidney and liver function and may also reveal tumor markers, although these are not very reliable for breast cancer.
  • A biopsy of the tumor will be used to assess certain characteristics that can tell the doctor how aggressive the cancer is. Typically, lymph nodes are biopsied as well.
  • Chest X-rays can show if the cancer has spread to the lungs.
  • Bone scans can reveal whether there's cancer in the bones.
  • CT scans are used to look at the chest and abdomen to see if the cancer has spread to other organs.
  • Sometimes PET scans are used to check for cancer in the lymph nodes or to scan the whole body for cancer.
  • The doctor may ask for an MRI if she's concerned about whether cancer has spread to the brain.
  • The doctor will ask about the patient's family history and may recommend a new test called Oncotype DX , which is used to predict the likelihood of breast cancer recurrence. It can be a useful tool for women with early-stage cancer who are trying to decide whether chemotherapy is necessary.

How breast cancer is diagnosed and staged

Oncologists use a complex system of letters and numerals to determine the status or stage of breast cancer. Knowing these numbers is very important, because it will help the patient understand the prognosis. If your friend or relative wants you to accompany her to doctor visits, you can help her understand what you both hear there. You'll also want to know as much as possible in order to research and understand treatment options and explore clinical trials.

The letter T is used to designate the tumor size and spread, the word N indicates whether there's cancer present in the lymph nodes, and the letter M stands for metastasis. So T2, N0 (zero), M0 means a 2-centimeter tumor that has not spread to the lymph nodes or any other areas.

The medical team then combines this information into a stage. There are four stages of invasive breast cancer, and some stages are broken down still further:

Stage 1

The tumor is smaller than 2 centimeters and no lymph nodes are involved.

Stage IIA

There are three possibilities at this stage:

  • The tumor measures less than 2 centimeters but has spread to the axillary lymph nodes.
  • No tumor is found in the breast itself, but cancer cells are found in the lymph nodes under the arm.
  • The tumor is between 2 and 5 centimeters across but there's no lymph node involvement.

Stage IIB

There are two possibilities at this stage:

  • The tumor is 2 to 5 centimeters across and has spread to the axillary lymph nodes.
  • The tumor is bigger than 5 centimeters but hasn't spread to the lymph nodes.

Stage IIIA

There are two possibilities at this stage:

  • The tumor has spread to the axillary lymph nodes and the nodes are clumped together or sticking to other structures.
  • No tumor is found in the breast, but cancer is in the lymph nodes, which are clumping together or sticking to other structures, or it is present in lymph nodes near the breastbone.

Stage IIIB

There are two possibilities at this stage:

  • A tumor of any size has spread to the chest wall or skin of the breast; it also may have spread to axillary lymph nodes or those near the breastbone.
  • All inflammatory breast cancer, which is considered Stage IIIB or higher when diagnosed.

Stage IV

The cancer has spread to other organs of the body, usually the lungs, brain, or liver; or the bones. Sometimes the doctor will say the cancer is metastatic at presentation , which means it had already spread to other parts of the body before the original tumor was discovered.

Understanding the importance of hormonal status

Oncologists and other cancer specialists look at whether breast cancer cells have certain characteristics that can predict aggressive growth. Pathology results from the biopsy will determine:

  • Whether the cancer has receptors for the hormones estrogen and progesterone. You'll hear the doctor use the terms ER-positive or ER-negative , which means the tumor tested positive or negative for an abundance of estrogen receptors.
  • The amount of a protein called HER-2 produced by cancer cells. A HER-2 positive tumor is considered to be more aggressive, but it also means your family member can take Herceptin, a new drug that treats HER-2 positive tumors with excellent success.

Information about hormonal receptor status and HER-2 status can help the doctor recommend an individualized treatment plan that will offer the best chance of curing or controlling the cancer.

Assessing the outlook for breast cancer

Once the medical team has assembled all the information possible to determine staging, it will offer a prognosis. This can be a tricky business, as there are many variables that affect a woman's health and response to breast cancer treatment.

Sometimes doctors will discuss prognosis in terms of statistical "cure rates," "recurrence rates," or "survival rates." This can sound very impersonal, but it's the medical profession's way of offering its best guess in terms of what you can expect.

One measure commonly used is the 5-year survival rate , which means the percentage of those who live at least five years after being diagnosed. Keep in mind that many of these patients live considerably longer than five more years, but they may be tracked for only five years.

Another term is 5-year relative survival rate , which takes into account the fact that some patients with cancer will die from other causes. Many organizations are adopting this number, as it's considered more accurate.

Assuming you're invited to your family member's doctor visits, pay close attention when her doctor gives her this information, and ask as many questions as you need to in order to understand the information. A person who's still reeling from a cancer diagnosis may have trouble taking in what she hears.

For example, the doctor may tell her that among all people with breast cancer , five-year relative survival is 100 percent for stage I, 86 percent for stage II, 57 percent for stage III, and 20 percent for stage IV. But these are very general numbers -- her doctor can use information about tumor characteristics and general health to offer her a better sense of her own breast cancer and put these statistics in perspective.