The short answer
Breast cancer is cancer that starts in the breast, when cells there grow without control and form a tumor. It mostly affects women aged 45 and older, but anyone with breasts can get it. Mammograms can find it early, and there are many types depending on where it begins and how far it has spread.
Breast cancer starts when cells in the breast grow without control and form a tumor that may spread.
It can start in the milk ducts, the milk-making lobules, the nipple, or other breast tissue.
Most breast cancers begin in the ducts and are called ductal cancers.
Breast cancer mostly affects women aged 45 and older, but anyone with breasts can get it; it is rare in children and men.
Subjective: What you might experience
This section describes the symptoms and history a patient might report to their doctor.
A new lump or thickening in the breast or underarm.
Change in breast size or shape, dimpling, or skin that looks like an orange peel.
Nipple changes
turning inward, discharge (especially bloody), scaling, or redness.
Breast or nipple pain that does not go away.
Often no symptoms
found on a screening mammogram before it can be felt.
Risk history
age, family history, inherited gene changes (BRCA1/BRCA2), prior chest radiation, hormone exposure.
Objective: Tests and findings
Clinical breast exam of both breasts and the lymph nodes under the arm and near the collarbone.
Diagnostic mammogram and breast ultrasound; breast MRI in selected cases.
Biopsy of the suspicious area (needle biopsy) for tissue diagnosis — the definitive test.
Pathology tests for hormone receptors (ER/PR) and HER2, plus grade.
Imaging to check for spread when indicated.
Interactive anatomy guide
Explore where cancers start and how they are found, on an interactive body map.
Open the anatomy guideAssessment: Staging and prognosis
Diagnosis confirmed by biopsy; classified as in situ (contained) versus invasive.
Staged with the TNM system combined with tumor grade and receptor status.
Receptor and HER2 status (e.g., hormone-receptor-positive, triple-negative) directly shape treatment.
Nodal status and any distant spread assessed to determine overall stage.
Plan: The treatment approach
Surgery
lumpectomy (breast-conserving) or mastectomy, often with lymph node evaluation.
Radiation therapy after breast-conserving surgery or for higher-risk disease.
Systemic therapy tailored to biology
hormone therapy, HER2-targeted therapy, chemotherapy, or immunotherapy.
Genetic counseling when inherited risk is suspected.
Follow-up exams, imaging, and survivorship care.
These are simplified, educational SOAP-style summaries showing the kinds of findings clinicians document when evaluating each cancer, based on National Cancer Institute resources. They describe typical diagnostic criteria and workups — not a real patient, and not medical advice. Real clinical notes are individualized. Always rely on your own care team. Based on National Cancer Institute educational content. Educational only — not medical advice.
Words to know
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Common questions
Where does breast cancer start?
Breast cancer starts in the breast, and it can begin in one or both breasts. It can form in glandular tissue (the milk ducts and lobules), in the fibrous and fatty tissue that gives the breast its shape, in the nipple, or in the blood and lymph vessels of the breast. Most breast cancers start in the ducts.
Who can get breast cancer?
Breast cancer mostly affects females aged 45 and older, but anyone with breasts can get it. It is rare in children and in men.
What is the difference between carcinoma in situ and invasive breast cancer?
When the abnormal cells stay within the ducts or lobules and have not spread to other breast tissue, it is called carcinoma in situ. Invasive cancers have spread into the surrounding breast tissue and can spread to nearby lymph nodes or other organs. Most breast cancers are invasive.
Are there different types of breast cancer?
Yes. There are many types, depending on where the cancer begins and how far it has spread. Cancers that start in the ducts are called ductal cancers, and cancers that start in the lobules are called lobular cancers. Less common types include inflammatory breast cancer, Paget disease of the breast, and phyllodes tumor.
Can breast cancer be found early?
Yes. Mammograms can detect breast cancer early, possibly before it has spread. Finding cancer early can make it easier to treat.
Questions to ask your doctor
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Sources last checked: 2026-07-21 what this meansLast updated: 2026-07-21Next planned review: 2027-07-21
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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