What Is Breast Cancer?

Breast cancer is a type of cancer that starts in the breast. It can start in one or both breasts.

How breast cancer starts

Breast cancer occurs almost entirely in women, but men can get breast cancer, too.

Cancer starts when cells begin to grow out of control. 

It’s important to understand that most breast lumps are benign and not cancerous (malignant). Non-cancerous breast tumors are abnormal growths, but they do not spread outside of the breast. They are not life-threatening, but some types of benign breast lumps can increase a woman's risk of getting breast cancer.

Any breast lump or change needs to be checked by a health care professional to find out if it is benign or malignant (cancer) and if it might affect your future cancer risk. 

Where breast cancer starts

Breast cancer can start from different parts of the breast. The breast is an organ that sits on top of the upper ribs and chest muscles. There is a left and right breasts, and each one has mainly glands, ducts, and fatty tissue. In women, the breast makes and delivers milk to feed newborns and infants. The amount of fatty tissue in the breast determines the size of each breast.

The breast has different parts:

• Lobules are the glands that make breast milk. Cancers that start here are called lobular cancers.
• Ducts are small canals that come out from the lobules and carry the milk to the nipple. This is the most common place for breast cancer to start. Cancers that start here are called ductal cancers.
• The nipple is the opening in the skin of the breast where the ducts come together and turn into larger ducts so the milk can leave the breast. The nipple is surrounded by slightly darker, thicker skin called the areola. A less common type of breast cancer, called Paget's disease of the breast, can start in the nipple.
• The fat and connective tissue (stroma) surround the ducts and lobules and help keep them in place. A less common type of breast cancer, called a phyllodes tumor, can start in the stroma.
• Blood vessels and lymph vessels are also found in each breast. Angiosarcoma is a less common type of breast cancer that can start in the lining of these vessels. The lymph system is described below.

A small number of cancers originate in tissues other than the breast. These cancers are called sarcomas and lymphomas and are not thought of as breast cancers.

How breast cancer spreads

Breast cancer can spread when the cancer cells get into the blood or lymph system and then are carried to other parts of the body. 

The lymph (or lymphatic) system is a part of your body's immune system. It is a network of lymph nodes (small, bean-sized glands), ducts or vessels, and organs that work together to collect and carry clear lymph fluid through the body tissues to the blood. The clear lymph fluid inside the lymph vessels contains tissue by-products and waste material, as well as immune system cells.

The lymph vessels carry lymph fluid away from the breast. In the case of breast cancer, cancer cells can enter those lymph vessels and start to grow in lymph nodes. Most of the lymph vessels of the breast drain into:

• Lymph nodes under the arm (axillary lymph nodes)
• Lymph nodes inside the chest near the breastbone (internal mammary lymph nodes)
• Lymph nodes around the collar bone (supraclavicular [above the collar bone] and infraclavicular [below the collar bone] lymph nodes)

If cancer cells have spread to your lymph nodes, there is a higher chance that the cells could have traveled through the lymph system and spread (metastasized) to other parts of your body. Still, not all women with cancer cells in their lymph nodes develop metastases, and some women with no cancer cells in their lymph nodes might develop metastases later.

Types of breast cancer

There are many different types of breast cancer. The type is determined by the specific kind of cells in the breast that are affected. Most breast cancers are carcinomas. The most common breast cancers such as ductal carcinoma in situ (DCIS) and invasive carcinoma are adenocarcinomas, since the cancers start in the gland cells in the milk ducts or the lobules (milk-producing glands). Other kinds of cancers can grow in the breast, like angiosarcoma or sarcoma, but are not considered breast cancer since they start in different cells of the breast.

Breast cancers are also classified by certain types of proteins or genes each cancer might make. After a biopsy is done, breast cancer cells are tested for proteins called estrogen receptors and progesterone receptors, and the HER2 gene or protein. The tumor cells are also closely looked at in the lab to find out what grade it is. The specific proteins found and the tumor grade can help decide the stage of the cancer and treatment options.

What Causes Breast Cancer?

We don't know what causes each case of breast cancer. But we do know many of the risk factors for these cancers. We also know that normal breast cells can become cancerous because of changes or mutations in genes. Hormones also seem to play a role in many cases of breast cancer, but just how this happens is not fully understood.

Lifestyle-related risk factors

Lifestyle-related risk factors, such as what you eat and how much you exercise, can increase your chance of developing breast cancer, but it’s not yet known exactly how some of these risk factors cause normal cells to become cancerous.

Hormones

Hormones also seem to play a role in many cases of breast cancer, but just how this happens is not fully understood.

Gene mutations

We do know that normal breast cells can become cancerous because of changes or mutations in genes. But only about 1 in 10 breast cancers (10%) are linked with known abnormal genes that are passed on from parents (inherited). Many genes have not yet been discovered, so women with a family history of breast cancer might have inherited an abnormal gene that doesn't show on a genetic test. Most breast cancers (about 90%) develop from acquired (not inherited) gene changes that have not yet been identified. 

How gene changes can lead to breast cancer

Genes control how our cells function. They are composed of a chemical called DNA, which is inherited from both parents. DNA affects more than just how we look; it also can influence our risk for developing certain diseases, including some kinds of cancer. Normal cells have genes called proto-oncogenes, which help control when the cells grow, divide to make new cells, or stay alive. If a proto-oncogene is mutated (changed) in a certain way, it becomes an oncogene. Cells that have these mutated oncogenes can become cancerous. Normal cells also have genes called tumor suppressor genes, which help control how often normal cells divide in two, repair DNA mistakes, or cause cells to die at the right time. If a cell has a mutated tumor suppressor gene, then the cell can turn into cancer. Cancers can be caused by gene changes that turn on oncogenes or turn off tumor suppressor genes. Changes in many different genes are usually needed to cause breast cancer.

Inherited gene changes

Some gene changes (mutations) are inherited or passed to you from your parents. This means the mutations are in all your cells when you are born. Certain inherited gene changes can greatly increase the risk of developing certain cancers and are linked to many of the cancers that run in some families. For instance, the BRCA genes (BRCA1 and BRCA2) are tumor suppressor genes. When one of these genes changes, it no longer suppresses abnormal cell growth, and cancer is more likely to develop. A change in one of these genes can be passed from a parent to a child.

Women have already begun to benefit from advances in understanding the genetic basis of breast cancer. Genetic testing can identify some women who have inherited mutations in the BRCA1 or BRCA2 tumor suppressor genes as well as other less common genes such as PALB2, ATM, or CHEK2. These women can then take steps to reduce their risk of breast cancer by increasing awareness of their breasts and following appropriate screening recommendations to help find cancer at an earlier, more treatable stage. Since these mutations are also often associated with other cancers (besides breast), women with these mutations might also consider early screening and preventive actions for other cancers.

Mutations in tumor suppressor genes like the BRCA genes are considered “high penetrance” because they often lead to cancer. Although many women with high penetrance mutations develop cancer, most cases of cancer (including breast cancer) are not caused by this kind of mutation.

More often, low-penetrance mutations or gene variations are a factor in cancer development. Each of these may have a small effect on cancer occurring in any one person, but the overall effect on the population can be large because the mutations are common, and people often have more than one at the same time. The genes involved can affect things like hormone levels, metabolism, or other factors that impact risk for breast cancer. These genes might also cause much of the risk of breast cancer that runs in families.

Acquired gene changes

Most gene mutations linked to breast cancer are acquired. This means the change takes place in breast cells during a person's life rather than having been inherited or born with them. Acquired DNA mutations take place over time and are only in the breast cancer cells.

These acquired mutations of oncogenes and/or tumor suppressor genes may result from other factors, like radiation or cancer-causing chemicals. But some gene changes may just be random events that sometimes happen inside a cell, without having an outside cause. So far, the causes of most acquired mutations that could lead to breast cancer are still unknown. Most breast cancers have several acquired gene mutations.

Breast cancer early detection and diagnosis

Breast cancer is sometimes found after symptoms appear, but many women with breast cancer have no symptoms. This is why regular breast cancer screening is so important.  Different tests can be used to look for and diagnose breast cancer. If your doctor finds an area of concern on a screening test (a mammogram), or if you have symptoms that could mean breast cancer, you will need more tests (Breast Ultrasound, Breast MRI, Newer and Experimental Breast Imaging Tests) to know for sure if it’s cancer. The most common symptom of breast cancer is a new lump or mass, but other symptoms are also possible. It's important to have any breast changes checked by a healthcare provider. A biopsy is done when mammograms, other imaging tests, or a physical exam show a breast change that may be cancer. A biopsy is the only way to know for sure if it’s cancer. 

If you’ve been diagnosed with breast cancer, you’ve probably heard a lot of different terms used to describe your cancer. Doctors use information from your breast biopsy to learn a lot of important things about the exact kind of cancer you have. You may also need more tests to get more details, such as the stage of the cancer or how fast it’s growing. If you have been diagnosed with breast cancer, tests will be done to find out the extent (stage) of the cancer. The stage of a cancer helps determine how serious the cancer is and how best to treat it.

Treating Breast Cancer

If you’ve been diagnosed with breast cancer, your cancer care team will discuss your treatment options with you. It’s important that you think carefully about each of your choices and weigh the benefits of each treatment option against the possible risks and side effects. Some treatments, like surgery and radiation, are local, meaning they treat the tumor without affecting the rest of the body. 

Most women with breast cancer will have some type of surgery to remove the tumor. Depending on the type of breast cancer and how advanced it is, you might need other types of treatment as well, either before or after surgery, or sometimes both. Most usual are Surgery for Breast Cancer and Radiation for Breast Cancer. They can also be followed up with systematic therapies. Drugs used to treat breast cancer are considered systemic therapies because they can reach cancer cells almost anywhere in the body. Some can be given by mouth, injected into a muscle, or put directly into the bloodstream. Depending on the type of breast cancer, different types of drug treatment might be used, including: Chemotherapy for Breast Cancer, Hormone Therapy for Breast Cancer, Targeted Drug Therapy for Breast Cancer, and Immunotherapy for Breast Cancer.

Follow-up Care After Breast Cancer Treatment

After you complete your breast cancer treatment, your cancer care team will still want to watch you closely. It's important to understand your care schedule and go to all of your follow-up appointments. 

What to expect during follow-up care

Many women are relieved to be finished with breast cancer treatment, but also worry about the cancer coming back, and can feel lost when they don't see their cancer care team as often.

But for some women with advanced breast cancer, the cancer may never go away completely. These women may continue to get treatments to help keep the breast cancer under control and to help relieve symptoms from it. Learning to live with advanced breast cancer that doesn’t go away can have its types of stress and uncertainty.

Even if you have completed breast cancer treatment, your doctors still will want to watch you closely, so you need to go to all of your follow-up appointments. During these visits, your doctors will ask if you are having any problems and will examine you. Lab tests and imaging tests typically aren't needed after treatment for most early-stage breast cancers. But they might be done in some women who are having symptoms to see if they're the result of the cancer returning or are from treatment-related side effects.

Almost any cancer treatment can have side effects. Some might only last for a few days or weeks, but others might last a long time. Some side effects might not even show up until years after you have finished treatment. Your doctor visits are a good time for you to ask questions and talk about any changes or problems you notice or concerns you have. However, if concerns about your cancer come up between visits, you shouldn't wait until your next scheduled visit. Call your doctor's office right away.

Typical follow-up schedules

Your follow-up schedule can depend on many factors, including the type of breast cancer, how advanced it was when it was found (the stage of the cancer), and how it was (or is being) treated.

• Doctor visits: If you have finished treatment, your follow-up visits will probably be every few months at first. The longer you have been free of cancer, the less often the appointments are needed. After 5 years, they are typically done about once a year.
• Mammograms: If you had breast-conserving surgery (lumpectomy or partial mastectomy), you will probably have a mammogram about 6 to 12 months after surgery and radiation are completed, and then at least every year after that. Women who've had a mastectomy (removal of the entire breast) typically no longer need mammograms on that side. But unless you've had both breasts removed, you still need to have yearly mammograms on the remaining breast.
• Pelvic exams: If you are taking either of the hormone drugs tamoxifen or toremifene and still have your uterus, your doctor will likely recommend pelvic exams every year because these drugs can increase your risk of uterine (endometrial) cancer. This risk is highest in women who have gone through menopause. Be sure to tell your doctor right away about any unusual vaginal bleeding, such as bleeding or spotting after menopause, bleeding or spotting between periods, or a change in your periods. Although this is usually caused by something that isn’t cancer, it can also be the first sign of uterine cancer.
• Bone density tests: If you are taking a hormone drug called an aromatase inhibitor (such as anastrozole, letrozole, or exemestane) for early-stage breast cancer, or if treatment puts you into menopause, your doctor will want to monitor your bone health and may consider testing your bone density.
• Other tests: Other tests, such as blood tests and imaging tests (like bone scans, x-rays, or CT or PET scans), are not a standard part of follow-up for most women who've been treated for breast cancer, because they haven't been shown to help them live longer. But one or more of these tests might be done if you have symptoms or physical exam findings that suggest that the cancer might have come back.

If symptoms, exams, or tests suggest your cancer might have returned, imaging tests such as an X-ray, CT scan, PET scan, MRI scan, bone scan, and/or a biopsy may be done. If the cancer recurrence is confirmed, your doctor may also check your blood for circulating tumor cells (CTCs) or levels of blood tumor markers such as CA-15-3, CA 27-29, or CEA. Tumor marker levels go up in some women if their cancer recurs or has spread, so if a tumor marker level is high, your doctor might use it to monitor the results of further treatment. But tumor marker levels don’t go up in all women, so these tests aren't always helpful, and they aren't used to watch for cancer recurrence in women without any symptoms.

Ask your doctor for a survivorship care plan

Talk with your doctor about developing a survivorship care plan for you. This plan might include:

• A summary of your diagnosis, the tests that were done, and the treatment you received
• A suggested schedule for follow-up exams and tests
• A schedule for other tests you might need in the future, such as early detection (screening) tests for other types of cancer, or tests to look for long-term health effects from the breast cancer or its treatment
• A list of possible late- or long-term side effects from your treatment, including what to watch for and when you should contact your doctor
• Diet, physical activity, and other lifestyle modification suggestions

Keeping health insurance and copies of your medical records

Even after treatment is finished, it’s very important to keep your health insurance. Tests and doctor visits cost a lot, and even though no one wants to think their cancer might come back, this could happen.

At some point after your treatment, you might find yourself seeing a new doctor who doesn’t know about your medical history. It’s important to keep copies of your medical records so you can give your new doctor the details of your diagnosis and treatment.

If the cancer comes back

If cancer does return, your treatment options will depend on where it comes back, what treatments you've had before, and your current health and preferences.

It’s important to know that women who have had breast cancer can also still get other types of cancer, so it’s important to follow the  Cancer Society guidelines for the early detection of cancer, such as those for colorectal cancer and cervical cancer. Women who have had breast cancer are actually at higher risk for certain other cancers.