Breast cancer: Symptoms, causes, stages, types, and more

Breast cancer begins when abnormal cells in breast tissue grow out of control. It is often discussed as one disease, but it is actually a family of diseases with different starting points, biomarkers, growth rates, and treatment options. Two people with similarly sized tumors may therefore receive very different care plans.

In the United States, breast cancer is the most commonly diagnosed cancer among women, excluding some skin cancers. The American Cancer Society estimates that 321,910 women and 2,670 men will be diagnosed with invasive breast cancer in 2026. Those numbers are serious, but screening, earlier diagnosis, and increasingly precise therapies have improved outcomes for many patients.

Research support: American Cancer Society and SEER.

What is breast cancer?

The breast contains milk-producing lobules, ducts, fat, connective tissue, blood vessels, and lymph vessels. Most breast cancers begin in a duct or lobule. Cancer becomes invasive when malignant cells break through the structure where they started and enter surrounding tissue. From there, cells may reach nearby lymph nodes or distant organs. Anyone with breast tissue can develop the disease, although it is far more common in women.

Research support: NCI, Cleveland Clinic, CDC, and Johns Hopkins Medicine.

Breast cancer symptoms and warning signs

Early breast cancer may cause no symptoms and may first appear on a screening mammogram. A new lump is the best-known warning, but it is not the only one. Most breast changes are benign, yet a new or persistent change deserves medical evaluation rather than a month-long debate with the bathroom mirror.

Common symptoms

• A new lump, hard knot, or thickened area in the breast, chest, or underarm
• Swelling of all or part of a breast
• A change in breast size, shape, contour, or symmetry
• Dimpling, puckering, irritation, or orange-peel-like skin
• A nipple that newly turns inward
• Red, flaky, crusted, or thickened nipple or breast skin
• Discharge that is not breast milk, especially bloody or one-sided discharge
• Persistent breast or nipple pain
• Enlarged lymph nodes near the underarm or collarbone

A cancerous lump is often firm, irregular, and painless, but breast cancer can also feel soft, round, tender, or painful. Symptoms alone cannot confirm or rule out cancer.

Inflammatory breast cancer and symptoms in men

Inflammatory breast cancer may cause rapid swelling, heaviness, warmth, redness, discoloration, or skin dimpling without an obvious lump. Because it can resemble mastitis, symptoms that do not improve promptly need further evaluation. Men commonly notice a firm lump near the nipple, but nipple inversion, discharge, scaling, redness, or dimpling can also occur.

Research support: CDC, American Cancer Society, NCI, Susan G. Komen, MedlinePlus, Mayo Clinic, and Johns Hopkins Medicine.

What causes breast cancer?

Breast cancer develops after cells acquire DNA changes that disrupt normal controls on growth, repair, and cell death. The exact trigger is unknown in most cases. Risk usually reflects a combination of age, inherited biology, hormones, breast tissue characteristics, medical history, and lifestyle exposures. A risk factor raises probability; it does not guarantee disease, and a diagnosis is not proof that someone “did something wrong.”

Risk factors that cannot be changed

• Age: Risk rises over time.
• Inherited variants: Harmful changes in BRCA1, BRCA2, PALB2, CHEK2, TP53, PTEN, ATM, and other genes may increase risk.
• Family or personal history: Risk may be higher after breast cancer, certain high-risk breast lesions, or cancer in close relatives.
• Dense breasts: Dense tissue is linked to higher risk and can hide tumors on mammograms.
• Hormonal and reproductive history: Longer lifetime estrogen exposure can influence risk.
• Prior chest radiation: High-dose radiation at a young age raises later risk.

Potentially modifiable risk factors

• Drinking alcohol
• Low physical activity
• Excess body weight after menopause
• Some menopausal hormone therapy regimens

Research support: NCI, CDC, Mayo Clinic, American Cancer Society, FDA, and ACOG.

Main types of breast cancer

Ductal carcinoma in situ

Ductal carcinoma in situ, or DCIS, is stage 0. Abnormal cells remain inside a milk duct and have not invaded nearby tissue. DCIS is not immediately life-threatening, but some cases may progress, so treatment is usually recommended according to the lesion and the patient’s circumstances.

Invasive ductal and lobular carcinoma

Invasive ductal carcinoma, or IDC, begins in a duct and spreads into surrounding breast tissue. It is the most common invasive form. Invasive lobular carcinoma, or ILC, begins in a milk-producing lobule and may grow diffusely, causing thickening or fullness rather than a neat, easy-to-feel lump.

Inflammatory and other uncommon cancers

Inflammatory breast cancer grows through skin lymph vessels and usually causes rapid swelling and skin changes. Paget disease affects the nipple and areola. Other uncommon tumors include metaplastic, mucinous, tubular, and phyllodes tumors.

Hormone receptor and HER2 subtypes

Pathologists test invasive tumors for estrogen receptors, progesterone receptors, and HER2. Hormone receptor-positive cancers may respond to endocrine therapy. HER2-positive cancers may respond to HER2-targeted medicines. Triple-negative cancers lack all three markers; chemotherapy is often central, while immunotherapy or other targeted approaches may help selected patients.

Biomarkers can change treatment even when the stage is the same. For example, two stage II cancers may require different drug regimens because one is HER2-positive and the other is hormone receptor-positive and HER2-negative.

Research support: NCI, Mayo Clinic, Cleveland Clinic, Susan G. Komen, Johns Hopkins Medicine, and CDC.

Breast cancer stages

Staging combines the primary tumor, lymph-node involvement, distant spread, grade, and biomarkers. The familiar categories are:

• Stage 0: Noninvasive disease, usually DCIS, remains within a duct.
• Stage I: A small invasive cancer is limited to the breast or has minimal lymph-node involvement.
• Stage II: The tumor is larger, has reached nearby nodes, or both, without distant spread.
• Stage III: Locally advanced cancer involves extensive nodes, breast skin, or the chest wall.
• Stage IV: Metastatic cancer has spread to areas such as bone, liver, lungs, or brain.

Stage IV disease is generally treated as chronic and life-limiting rather than curable, but modern systemic therapy can shrink tumors, relieve symptoms, protect quality of life, and help some people live for years.

Research support: NCI, MedlinePlus, Cleveland Clinic, Susan G. Komen, and Johns Hopkins Medicine.

How breast cancer is diagnosed

An abnormal screening result is not a cancer diagnosis. Evaluation may include a clinical exam, diagnostic mammogram, ultrasound, and sometimes MRI. Imaging identifies suspicious areas, but a biopsy is required to confirm cancer.

A pathologist examines the tissue and reports the type, grade, hormone receptor status, HER2 status, and other features. Tests may evaluate lymph nodes or distant spread when appropriate. In some early hormone receptor-positive cancers, genomic tumor testing helps estimate recurrence risk or the likely value of chemotherapy. This differs from inherited genetic testing, which looks for variants that may affect relatives as well as the patient.

Research support: NCI, CDC, MedlinePlus, Susan G. Komen, and Mayo Clinic.

Breast cancer treatment

Treatment depends on stage, tumor biology, age, overall health, prior therapy, pregnancy status, and personal priorities. A plan may combine local treatment with medicines that travel through the bloodstream.

Local treatments

• Surgery: Lumpectomy removes the tumor with surrounding tissue; mastectomy removes most or all breast tissue. Lymph nodes may also be checked.
• Radiation: Radiation lowers local recurrence risk and is commonly used after lumpectomy and in selected patients after mastectomy.

Systemic treatments

• Endocrine therapy blocks estrogen signaling or lowers estrogen in hormone receptor-positive disease.
• Chemotherapy may be used before surgery, after surgery, or to control metastatic cancer.
• Targeted therapy attacks features such as HER2 or specific mutations.
• Immunotherapy may help selected triple-negative cancers.

Not everyone needs chemotherapy, and mastectomy is not automatically better than breast-conserving treatment for every early cancer. The best plan is the one supported by evidence for that tumor and that personnot necessarily the option with the most dramatic name.

Research support: NCI, CDC, Mayo Clinic, Cleveland Clinic, MedlinePlus, and Johns Hopkins Medicine.

Screening and ways to lower risk

No strategy prevents every breast cancer. Risk may be reduced by limiting alcohol, staying active, maintaining a healthy weightespecially after menopauseand reviewing menopausal hormone therapy with a clinician.

For average-risk women, the U.S. Preventive Services Task Force recommends mammography every two years from ages 40 through 74. The American College of Obstetricians and Gynecologists recommends beginning at 40 and screening every one to two years. Guidelines vary slightly, so timing should reflect personal risk and shared decision-making.

People with a harmful inherited variant, strong family history, prior high-dose chest radiation, or another high-risk condition may need earlier mammography and breast MRI. Dense tissue raises risk and can make cancer harder to see; mammography reports must now tell patients whether their breasts are dense. Breast awareness can help identify changes, but it does not replace imaging, and thermography is not a substitute for mammography.

Research support: USPSTF, ACOG, ACS, NCI, FDA, and CDC.

Outlook and survival

Outlook depends on stage, subtype, grade, age, health, response to treatment, and access to care. Recent SEER data report five-year relative survival of 100% for localized female breast cancer, 87.5% for regional disease, and 33.8% for distant disease. These are population averages, not predictions for one person, and they may not fully reflect the newest treatments.

Research support: SEER and NCI.

When to contact a health care professional

Arrange an appointment for any new breast, nipple, chest, or underarm change that persists or concerns youeven after a recent normal mammogram. Seek prompt evaluation for rapidly developing redness, swelling, warmth, skin dimpling, or nipple changes. After diagnosis, report fever, uncontrolled pain, breathing difficulty, new neurologic symptoms, severe side effects, or signs of infection to the care team.

Conclusion

Breast cancer is not one uniform illness. Symptoms can include lumps, skin changes, nipple changes, swelling, pain, or no warning signs at all. Stage and biomarkers guide treatment, while mammography can detect disease before it is felt and biopsy confirms the diagnosis. The practical takeaway is to understand personal risk, follow an appropriate screening plan, and have new changes evaluated. Early attention does not create bad news; it creates informationand information creates more room to act.

Experiences people may have during the breast cancer journey

No two breast cancer experiences are identical, but certain moments appear repeatedly in patient stories. A person may attend a routine mammogram expecting to return to work before lunch, then receive a request for additional images. The phrase “we need another look” can turn an ordinary Tuesday into a mental marathon. Most callbacks do not end in cancer, yet waiting still feels enormous. Asking when results should arrive and writing down the next step can keep uncertainty from filling every available thought.

If a biopsy confirms cancer, medical vocabulary arrives quickly: grade, stage, margins, receptors, HER2, nodes, and genomic score. Many patients hear only fragments during the first appointment. Bringing a trusted person, taking notes, or requesting a written summary can help. One useful question is, “What do we know now, and what are we still waiting to learn?” That separates confirmed facts from possibilities and keeps the alphabet soup from taking over the entire kitchen.

Treatment experiences vary. Someone having a lumpectomy and radiation may continue working with schedule changes. Another person receiving chemotherapy before surgery may need transportation, meals, child care, or help at home. Fatigue can be especially frustrating because it is invisible and unpredictable. A concrete offerdriving to Tuesday’s infusion or leaving dinner at the dooris often easier to accept than the well-meant but vague “Tell me what you need.”

Hair loss, scars, numbness, breast asymmetry, mastectomy, weight changes, early menopause, or sexual side effects can affect identity and confidence. Gratitude for effective treatment and grief about body changes can coexist. Some people choose reconstruction, some use a prosthesis, and others prefer a flat closure. The right decision is the one made with accurate information and respect for the patient’s priorities.

After active treatment, celebration may mix with fear of recurrence. Survivorship care can include follow-up visits, rehabilitation, management of long-term effects, mental health support, and instructions about symptoms that require a call. People living with metastatic breast cancer often face continuing treatment, repeated scans, and changing drug regimens while still working, parenting, traveling, and pursuing meaningful goals. Palliative care can improve comfort and quality of life at any stage; it is support, not surrender.

A useful principle is to make the next decision rather than every decision at once. Ask for plain-language explanations, seek a second opinion when needed, and let others help in specific ways. Breast cancer may reorganize a calendar, a body, and a sense of certainty, but it does not erase the person who had plans before the diagnosisor the possibility of making new ones afterward.

Note: This article is for general educational purposes and does not replace diagnosis, screening advice, or treatment recommendations from a qualified health care professional. Anyone with a new or concerning breast change should seek medical evaluation.