What Is Breast Cancer?
Breast cancer is a type of cancer that starts in the breast. Cancer starts when cells begin to grow out of control. (To learn more about how cancers start and spread, see What Is Cancer?)
Breast cancer cells usually form a tumor that can often be seen on an x-ray or felt as a lump. Breast cancer occurs almost entirely in women, but men can get breast cancer, too.
It’s important to understand that most breast lumps are benign and not cancer (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 determine if it is benign or malignant (cancer) and if it might affect your future cancer risk. See Non-cancerous Breast Conditions to learn more.
Where breast cancer starts
Breast cancers can start from different parts of the breast.
- Most breast cancers begin in the ducts that carry milk to the nipple (ductal cancers)
- Some start in the glands that make breast milk (lobular cancers)
- There are also other types of breast cancer that are less common like phyllodes tumor and angiosarcoma
- A small number of cancers start in other tissues in the breast. These cancers are called sarcomas and lymphomas and are not really thought of as breast cancers.
Although many types of breast cancer can cause a lump in the breast, not all do. See Breast Cancer Signs and Symptoms to learn what you should watch for and report to a health care provider. Many breast cancers are also found on screening mammograms, which can detect cancers at an earlier stage, often before they can be felt, and before symptoms develop.
Types of breast cancer
There are several different types of breast cancer, including:
- Ductal carcinoma: This begins in the milk duct and is the most common type.
- Lobular carcinoma: This starts in the lobules.
Invasive breast cancer occurs when the cancer cells break out from inside the lobules or ducts and invade nearby tissue. This increases the chance of cancer spreading to other parts of the body.
Noninvasive breast cancer develops when the cancer remains inside its place of origin and has not yet spread. However, these cells can sometimes progress to invasive breast cancer.
Once a biopsy is done, breast cancer cells are tested for proteins called estrogen receptors, progesterone receptors and HER2. 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 treatment options.
To learn more about specific types of breast cancer and tests done on the breast cancer cells, see Understanding a Breast Cancer Diagnosis.
How breast cancer spreads
Breast cancer can spread when the cancer cells get into the blood or lymph system and are carried to other parts of the body.
The lymph system is a network of lymph (or lymphatic) vessels found throughout the body that connects lymph nodes (small bean-shaped collections of immune system cells). The clear fluid inside the lymph vessels, called lymph, 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 nodes)
- Lymph nodes around the collar bone (supraclavicular [above the collar bone] and infraclavicular [below the collar bone] lymph nodes)
- Lymph nodes inside the chest near the breast bone (internal mammary 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. The more lymph nodes with breast cancer cells, the more likely it is that the cancer may be found in other organs. Because of this, finding cancer in one or more lymph nodes often affects your treatment plan. Usually, you will need surgery to remove one or more lymph nodes to know whether the cancer has spread.
Still, not all women with cancer cells in their lymph nodes develop metastases, and some women with no cancer cells in their lymph nodes develop metastases later.
The first symptoms of breast cancer usually appear as an area of thickened tissue in the breast or a lump in the breast or an armpit.
Other symptoms include:
- pain in the armpits or breast that does not change with the monthly cycle
- pitting or redness of the skin of the breast, similar to the surface of an orange
- a rash around or on one of the nipples
- discharge from a nipple, possibly containing blood
- a sunken or inverted nipple
- a change in the size or shape of the breast
- peeling, flaking, or scaling of the skin on the breast or nipple
Most breast lumps are not cancerous. However, women should visit a doctor for an examination if they notice a lump on the breast.
There are different ways of staging breast cancer. One way is from stage 0–4, with subdivided categories at each numbered stage. Descriptions of the four main stages are listed below, though the specific substage of a cancer may also depend on other specific characteristics of the tumor, such as HER2 receptor status.
- Stage 0: Known as ductal carcinoma in situ (DCIS), the cells are limited to within the ducts and have not invaded surrounding tissues.
- Stage 1: At this stage, the tumor measures up to 2 centimeters (cm) across. It has not affected any lymph nodes, or there are small groups of cancer cells in the lymph nodes.
- Stage 2: The tumor is 2 cm across, and it has started to spread to nearby nodes, or is 2–5 cm across and has not spread to the lymph nodes.
- Stage 3: The tumor is up to 5 cm across, and it has spread to several lymph nodes or the tumor is larger than 5 cm and has spread to a few lymph nodes.
- Stage 4: The cancer has spread to distant organs, most often the bones, liver, brain, or lungs.
After puberty, a woman’s breast consists of fat, connective tissue, and thousands of lobules. These are tiny glands that produce milk for breastfeeding. Tiny tubes, or ducts, carry the milk toward the nipple.
Cancer causes the cells to multiply uncontrollably. They do not die at the usual point in their life cycle. This excessive cell growth causes cancer because the tumor uses nutrients and energy and deprives the cells around it.
Breast cancer usually starts in the inner lining of milk ducts or the lobules that supply them with milk. From there, it can spread to other parts of the body.
The exact cause of breast cancer remains unclear, but some risk factors make it more likely. It is possible to prevent some of these risk factors.
The risk of breast cancer increases with age. At 20 years, the chance of developing breast cancer in the next decade is 0.06%. By the age of 70 years, this figure goes up to 3.84%.
Women who carry certain mutations in the BRCA1 and BRCA2 genes have a higher chance of developing breast cancer, ovarian cancer, or both. People inherit these genes from their parents.
Mutations in the TP53 gene also have links to increased breast cancer risk.
If a close relative has or has had breast cancer, a person’s chance of developing breast cancer increases.
Current guidelines recommend that people in the following groups seek genetic testing:
- those with a family history of breast, ovarian, fallopian tube, or peritoneal cancer
- those in whose ancestry there is a history of breast cancer related to BRCA1 or BRCA2 gene mutations, for example, people with Ashkenazi Jewish ancestry
3. A history of breast cancer or breast lumps
Women who have previously had breast cancer are more likely to have it again than those who have no history of the disease.
Having some types of noncancerous breast lump increases the chance of developing cancer later on. Examples include atypical ductal hyperplasia or lobular carcinoma in situ.
Individuals with a history of breast, ovarian, fallopian tube, or peritoneal cancer should ask their doctors about genetic testing.
4. Dense breast tissue
Women with more dense breasts are more likely to receive a diagnosis of breast cancer.
5. Estrogen exposure and breastfeeding
Extended exposure to estrogen appears to increase the risk of breast cancer.
This could be due to a person starting their periods earlier or entering menopause at a later than average age. Between these times, estrogen levels are higher.
Breastfeeding, especially for over 1 year, appears to reduce the chance of developing breast cancer. This is possibly due to the drop in estrogen exposure that follows pregnancy and breastfeeding.
6. Body weight
Women who become overweight or develop obesity after menopause may also have a higher chance of developing breast cancer, possibly due to increased estrogen levels. High sugar intake may also be a factor.
7. Alcohol consumption
A higher rate of regular alcohol consumption appears to play a role in breast cancer development.
According to the National Cancer Institute (NCI), studies have consistently found that women who consume alcohol have a higher risk of breast cancer than those who do not. Those who drink moderate to heavy levels of alcohol have a higher risk than light drinkers.
8. Radiation exposure
Undergoing radiation treatment for a different cancer may increase the risk of developing breast cancer later in life.
9. Hormone treatments
According to the NCI, studies have shown that oral contraceptives may slightly increase the risk of breast cancer
Cosmetic implants and breast cancer survival
A 2013 review found that women with cosmetic breast implants who received a diagnosis of breast cancer also had a higher risk of dying from the disease.
This could be due to the implants masking cancer during screening or because the implants bring about changes in breast tissue.
However, a 2015 review published in Aesthetic Surgery Journal found that having cosmetic breast implant surgery did not increase the risk of breast cancer.
Scientists need to carry out more research to confirm the link.
A doctor often diagnoses breast cancer as the result of routine screening or when a woman approaches her doctor after detecting symptoms.
Several diagnostic tests and procedures help to confirm a diagnosis.
The doctor will check the breasts for lumps and other symptoms.
During the examination, the person may need to sit or stand with their arms in different positions, such as above their head or by their sides.
Several tests can help detect breast cancer.
Mammogram: This is a type of X-ray that doctors commonly use during an initial breast cancer screening. It produces images that can help a doctor detect any lumps or abnormalities.
A doctor will usually follow any suspicious results with further testing. However, mammography sometimes shows a suspicious area that turns out not to be cancer.
Ultrasound: This scan uses sound waves to help a doctor differentiate between a solid mass and a fluid-filled cyst.
MRI: Magnetic Resonance Imaging (MRI) combines different images of the breast to help a doctor identify cancer or other abnormalities. A doctor may recommend an MRI as a follow-up to a mammogram or ultrasound. Doctors sometimes use them as a screening tool for those at higher risk of breast cancer.
In a biopsy, the doctor extracts a sample of tissue and sends it for laboratory analysis.
This shows whether the cells are cancerous. If they are, a biopsy indicates which type of cancer has developed, including whether or not the cancer is hormone sensitive.
Diagnosis also involves staging the cancer to establish:
- the size of a tumor
- how far it has spread
- whether it is invasive or noninvasive
Staging provides a picture of a person’s chances of recovery and their ideal course of treatment.
Treatment will depend on several factors, including:
- the type and stage of the cancer
- the person’s sensitivity to hormones
- the age, overall health, and preferences of the individual
The main treatment options include:
Factors affecting the type of treatment a person has will include the stage of the cancer, other medical conditions, and their individual preference.
If surgery is necessary, the type will depend on both the diagnosis and individual preference. Types of surgery include:
Lumpectomy: This involves removing the tumor and a small amount of healthy tissue around it.
A lumpectomy can help prevent the spread of the cancer. This may be an option if the tumor is small and easy to separate from its surrounding tissue.
Mastectomy: A simple mastectomy involves removing the lobules, ducts, fatty tissue, nipple, areola, and some skin. In some types, a surgeon will also remove the lymph nodes and muscle in the chest wall.
Sentinel node biopsy: If breast cancer reaches the sentinel lymph nodes, which are the first nodes to which a cancer can spread, it can spread into other parts of the body through the lymphatic system. If the doctor does not find cancer in the sentinel nodes, then it is usually not necessary to remove the remaining nodes.
Axillary lymph node dissection: If a doctor finds cancer cells in the sentinel nodes, they may recommend removing several lymph nodes in the armpit. This can prevent the cancer from spreading.
Reconstruction: Following mastectomy, a surgeon can reconstruct the breast to look more natural. This can help a person cope with the psychological effects of breast removal.
The surgeon can reconstruct the breast at the same time as performing a mastectomy or at a later date. They may use a breast implant or tissue from another part of the body.
A person may undergo radiation therapy around a month after surgery. Radiation involves targeting the tumor with controlled doses of radiation that kill any remaining cancer cells.
A doctor may prescribe cytotoxic chemotherapy drugs to kill cancer cells if there is a high risk of recurrence or spread. When a person has chemotherapy after surgery, doctors call it adjuvant chemotherapy.
Sometimes, a doctor may choose to administer chemotherapy before surgery to shrink the tumor and make its removal easier. Doctors call this neoadjuvant chemotherapy.
Hormone blocking therapy
Doctors use hormone blocking therapy to prevent hormone sensitive breast cancers from returning after treatment. Hormone therapy may be used to treat estrogen receptor (ER)-positive and progesterone receptor (PR)-positive cancers.
They usually administer hormone blocking therapy after surgery but might sometimes use it beforehand to shrink the tumor.
Hormone blocking therapy may be the only option for people who are not suitable candidates for surgery, chemotherapy, or radiotherapy.
Doctors may recommend a person has hormone therapy for 5–10 years after surgery. However, the treatment will not affect cancers that are not sensitive to hormones.
Examples of hormone blocking therapy medications may include:
- aromatase inhibitors
- ovarian ablation or suppression
- Goserelin, which is a luteinizing hormone-releasing agonist drug that suppresses the ovaries
Hormone treatment may affect fertility.
Targeted drugs can destroy specific types of breast cancer. Examples include:
- trastuzumab (Herceptin)
- lapatinib (Tykerb)
- bevacizumab (Avastin)
Treatments for breast and other cancers can have severe adverse effects. When deciding on a treatment, people should discuss the potential risks with a doctor and look at ways to minimize the side effects.
A person’s outlook with breast cancer depends on the staging. Early detection and treatment usually lead to a positive outlook.
According to the ACS, a person who receives treatment for stage 0 or stage 1 breast cancer has a 99% chance of surviving for at least 5 years after being diagnosed, when compared to women who do not have cancer.
If breast cancer reaches stage 4, the chance of surviving another 5 years reduces to around 27%.
Regular checks and screening can help detect symptoms early. Women should discuss their options with a doctor.
There are several different guidelines for how often women should have breast cancer screening.
The American College of Physicians (ACP) recommend that women aged 40–49 years with an average risk of breast cancer should discuss the benefits and risks of regular screenings with a doctor.
Between 50 and 74 years of age, women who have an average risk should undertake screenings every 2 years. Beyond 75 years of age, doctors only recommend screenings for women with a life expectancy of 10 or more years.
The ACS suggest that women of average risk can choose to have yearly scans from the age of 40 years onward. Those who have not should start annual screening at 45 years of age. They may decide to switch to screenings every other year when they reach 55 years of age.
The American College of Radiologists recommend screenings every year, starting from 40 years of age.
Despite the different recommendations, most experts agree that women should talk to their doctors about breast cancer screening from 40 years of age onward.
There is no way to prevent breast cancer. However, certain lifestyle decisions can significantly reduce the risk of breast cancer as well as other types.
- avoiding excessive alcohol consumption
- following a healthful diet containing plenty of fresh fruit and vegetables
- getting enough exercise
- maintaining a healthy body mass index (BMI)
Women should consider their options for breastfeeding and the use of HRT following menopause, as these can also increase the risk.
Preventive surgery is also an option for women at high risk of breast cancer.
The Breast Cancer Healthline app provides people with access to an online breast cancer community, where users can connect with others and gain advice and support through group discussions.
Which other cancers are common in women?
Other than skin cancer, the cancers that most often affect women include:
- lung cancer
- colorectal cancer
- uterine cancer
- thyroid cancer
- endometrial cancer
- cervical cancer
- ovarian cancer