Original source overview
What is breast cancer?Breast cancer is a cancer that starts in breast tissue. It happens when cells in the breast change and grow out of control. New cells grow even when you don't need them, and old cells don't die when they should. These extra cells can form a mass called a tumor.
Sometimes the cancer does not spread any further. This is called "in situ." If the cancer spreads outside the breast, the cancer is called "invasive." It may just spread to nearby tissues and lymph nodes. Or the cancer may metastasize (spread to other parts of the body) through the lymph system or the blood.
Breast cancer is the second most common type of cancer in women in the United States. Rarely, it can also affect men.
What are the types of breast cancer?There are different types of breast cancer. The types are based on which breast cells turn into cancer. The types include:
• Ductal carcinoma, which begins in the cells of the ducts. This is the most common type. • Lobular carcinoma, which begins in the lobules. It is more often found in both breasts than other types of breast cancer. • Inflammatory breast cancer, in which cancer cells block lymph vessels in the skin of the breast. The breast becomes warm, red, and swollen. This is a rare type. • Paget's disease of the breast, which is a cancer involving the skin of the nipple. It usually also affects the darker skin around the nipple. It is also rare.
What causes breast cancer?Breast cancer happens when there are changes in the genetic material (DNA). Often, the exact cause of these genetic changes is unknown.
But sometimes these genetic changes are inherited, meaning that you are born with them. Breast cancer that is caused by inherited genetic changes is called hereditary breast cancer.
There are also certain genetic changes that can raise your risk of breast cancer, including changes in the BRCA1 and BRCA2 genes. These two changes also raise your risk of ovarian and other cancers.
Besides genetics, your lifestyle and the environment can affect your risk of breast cancer.
Who is at risk for breast cancer?The factors that raise your risk of breast cancer include:
• Older age • History of breast cancer or benign (noncancer) breast disease • Inherited risk of breast cancer, including having BRCA1 and BRCA2 gene changes • Dense breast tissue • A reproductive history that leads to more exposure to the estrogen hormone, including:
• Menstruating at an early age • Being at an older age when you first gave birth or never having given birth • Starting menopause at a later age
• Taking hormone therapy for meopause • Radiation therapy to the breast or chest • Obesity • Drinking alcohol
What are the signs and symptoms of breast cancer?The signs and symptoms of breast cancer include
• A new lump or thickening in or near the breast or in the armpit. • A change in the size or shape of the breast. • A dimple or puckering in the skin of the breast. It may look like the skin of an orange. • A nipple turned inward into the breast. • Nipple discharge other than breast milk. The discharge might happen suddenly, be bloody, or happen in only one breast. • Scaly, red, or swollen skin in the nipple area or the breast. • Pain in any area of the breast.
How is breast cancer diagnosed?Your health care provider may use many tools to diagnose breast cancer and figure out which type you have:
• A physical exam, including a clinical breast exam (CBE). This involves checking for any lumps or anything else that seems unusual with the breasts and armpits. • A medical history. • Imaging tests, such as a mammogram, an ultrasound, or an MRI. • Breast biopsy. • Blood chemistry tests, which measure different substances in the blood, including electrolytes, fats, proteins, glucose (sugar), and enzymes. Some of the specific blood chemistry tests include a basic metabolic panel (BMP), a comprehensive metabolic panel (CMP), and an electrolyte panel.
If these tests show that you have breast cancer, you will have tests that study the cancer cells. These tests help your provider decide which treatment would be best for you. The tests may include:
• Genetic tests for genetic changes such in the BRCA and TP53 genes. • HER2 test. HER2 is a protein involved with cell growth. It is on the outside of all breast cells. If your breast cancer cells have more HER2 than normal, they can grow more quickly and spread to other parts of the body. • An estrogen and progesterone receptor test. This test measures the amount of estrogen and progesterone (hormones) receptors in cancer tissue. If there are more receptors than normal, the cancer is called estrogen and/or progesterone receptor positive. This type of breast cancer may grow more quickly.
Another step is staging the cancer. Staging involves doing tests to find out whether the cancer has spread within the breast or to other parts of the body. The tests may include other diagnostic imaging tests and a sentinel lymph node biopsy. This biopsy is done to see whether the cancer has spread to the lymph nodes.
What are the treatments for breast cancer?Treatments for breast cancer include:
• Surgery such as
• A mastectomy, which removes the whole breast • A lumpectomy to remove the cancer and some normal tissue around it, but not the breast itself
• Radiation therapy • Chemotherapy • Hormone therapy, which blocks cancer cells from getting the hormones they need to grow • Targeted therapy, which uses drugs or other substances that attack specific cancer cells with less harm to normal cells • Immunotherapy
Can breast cancer be prevented?You may be able to help prevent breast cancer by making healthy lifestyle changes such as:
• Staying at a healthy weight • Limiting alcohol use • Getting enough exercise • Limiting your exposure to estrogen by
• Breastfeeding your babies if you can • Limiting hormone therapy
If you are at high risk, your provider may suggest that you take certain medicines to lower the risk. Some women at very high risk may decide to get a mastectomy (of their healthy breasts) to prevent breast cancer.
It's also important to get regular mammograms. They may be able to identify breast cancer in the early stages, when it is easier to treat.
NIH: National Cancer Institute
Encyclopedic background — Wikipedia
The following selected excerpts provide background on “Breast cancer”. The scope here is Breast Cancer; it does not establish an individual diagnosis or treatment plan. They are not a substitute for the source overview or current local clinical guidance. Each excerpt below comes from the fixed Wikipedia revision [W1].
Definition and overview [W1]
Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include: a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a red or scaly patch of skin. In those with distant spread of the disease, there may be bone pain, swollen lymph nodes, shortness of breath, or yellow skin.
Risk factors for developing breast cancer include obesity, a lack of physical exercise, alcohol consumption, hormone replacement therapy during menopause, ionizing radiation, an early age at first menstruation, having children late in life (or not at all), older age, having a prior history of breast cancer, and a family history of breast cancer. About five to ten percent of cases are the result of an inherited genetic predisposition, including BRCA mutations among others. Breast cancer most commonly develops in cells from the lining of milk ducts and the lobules that supply these ducts with milk. Cancers developing from the ducts are known as ductal carcinomas, while those developing from lobules are known as lobular carcinomas. There are more than 18 other sub-types of breast cancer. The diagnosis of breast cancer is confirmed by taking a biopsy of the concerning tissue. Once the diagnosis is made, further tests are carried out to determine if the cancer has spread beyond the breast and which treatments are most likely to be effective.
Signs and symptoms [W1]
Most people with breast cancer have no symptoms at the time of diagnosis; a breast cancer screening test detects their tumor. For those who do have symptoms, a new lump in the breast is most common. Most breast lumps are not cancerous, though lumps that are painless, hard, and with irregular edges are more likely to be cancerous. Other symptoms include skin thickening known as peau d'orange swelling or pain in the breast; dimpling, thickening, redness, or dryness of the breast skin; and pain, or inversion of the nipple. Some may experience unusual discharge from the breasts, or swelling of the lymph nodes under the arms or along the collar bone.
Classification [W1]
Invasive tumor tissue is assigned a grade based on how distinct it appears from healthy breast. Breast tumors are graded on three features: the proportion of cancer cells that form tubules, the appearance of the cell nucleus, and how many cells are actively replicating. Each feature is scored on a three-point scale, with a higher score indicating less healthy-looking tissue. A grade is assigned based on the sum of the three scores. Combined scores of 3, 4, or 5 represent grade 1, a slower-growing cancer. Scores of 6 or 7 represent grade 2. Scores of 8 or 9 represent grade 3, a faster-growing, more aggressive cancer.
Risk factors [W1]
Up to 80% of the variation in breast cancer frequency across countries is due to differences in reproductive history
that impact a woman's levels of female sex hormones (estrogens). Women who begin menstruating earlier (before age 12) or who undergo menopause later (after 51) are at increased risk of developing breast cancer. Women who give birth early in life are protected from breast cancer – someone who gives birth as a teenager has around a 70% lower risk of developing breast cancer than someone who does not have children. That protection wanes with higher maternal age at first birth, and disappears completely by age 35. Breastfeeding also reduces one's chance of developing breast cancer, with an approximately 4% reduction in breast cancer risk for every 12 months of breastfeeding experience. Those who lack functioning ovaries have reduced levels of estrogens, and therefore greatly reduced breast cancer risk.
Reading this topic in context
Use “Breast Cancer” as a starting point for a focused discussion, rather than treating every statement in the broader encyclopedia article as applying to you. The original source overview and the background excerpts answer different questions: the overview explains the health topic for readers, while the encyclopedia supplies terminology and general context. Keep a record of which questions concern symptoms, a confirmed diagnosis, prevention, or an existing treatment. This helps a healthcare professional address the relevant issue without relying on an internet label.
Questions to take to a professional
1. What do the imaging, pathology and receptor results mean in this case?
2. What are the next diagnostic or treatment decisions and who coordinates them?
Evidence, scope and next steps
The health-topic overview is attributed to MedlinePlus / the National Library of Medicine at the original topic link below. Wikipedia [W1] is a secondary background source; its references can support further reading, but their presence is not evidence that WellPrimer has independently reviewed every study. No clinical review, guideline certification or NLM endorsement is claimed. For screening intervals, diagnostic thresholds, pregnancy or child-specific advice and treatment choices, check current guidance in your country with a qualified professional. Do not start, stop or change a prescribed medicine based on encyclopedia excerpts. New or worsening symptoms need appropriate clinical assessment rather than more reading alone.
Attribution and reuse
[W1] Wikipedia contributors, “Breast cancer”. Version 1380343909, edited 2026-10-15. Retrieved 2026-10-16. Fixed revision: https://en.wikipedia.org/w/index.php?title=Breast_cancer&oldid=1380343909. Contributor history: https://en.wikipedia.org/w/index.php?title=Breast_cancer&action=history. License: https://creativecommons.org/licenses/by-sa/4.0/ .
The MedlinePlus health-topic summary retains its original attribution. Wikipedia excerpts and the added compilation/commentary are shared under CC BY-SA 4.0; selections, section ordering and editorial reading prompts have been added. No images are reused. This is an educational compilation, not a clinician-reviewed guideline.