Overview & Definition

Breast cancer is a disease in which cells in the breast tissue grow abnormally and uncontrollably, potentially forming a tumor. In healthy tissue, cells grow and divide in a regulated way and older cells are replaced; in cancer, some cells acquire changes (mutations) that cause them to replicate when they shouldn’t and to evade normal cell death. These abnormal cells may remain confined to their original site (in situ, non-invasive) or invade nearby tissue and spread (metastasize) to lymph nodes or distant organs. While breast cancer occurs mainly in women, men can also develop it.

Anatomy & Where It Starts

The breast contains lobules (milk-producing glands), ducts (channels that carry milk to the nipple), and surrounding fatty and connective tissue (stroma). Most breast cancers begin in the ducts (ductal carcinoma) or lobules (lobular carcinoma). Much less commonly, cancers can arise in the stroma or the lining of blood/lymph vessels (for example, angiosarcoma).

Non-Invasive vs. Invasive

Non-invasive (in situ) cancers, such as ductal carcinoma in situ (DCIS), remain within their ducts or lobules. Invasive cancers break through the duct or lobule wall and infiltrate nearby tissue. Cancer cells can then enter lymphatic channels or the bloodstream and travel to other parts of the body, forming new tumors—a process called metastasis.

Causes & Risk Factors

• Age: risk rises as people get older.
• Inherited gene changes: such as BRCA1, BRCA2, and others (e.g., PALB2).
• Hormonal exposure: extended lifetime exposure to estrogen (e.g., early first period, late menopause, certain hormone therapies).
• Reproductive history: age at first childbirth, breastfeeding, and having no pregnancies.
• Breast density: dense tissue is associated with higher risk and can make screening harder to interpret.
• Lifestyle & environment: obesity (especially after menopause), alcohol, physical inactivity, prior chest radiation, and some exposures.
• Prior breast conditions: certain benign changes or a previous breast cancer.

Having risk factors does not mean someone will definitely develop breast cancer—and some people develop it without any known high-risk factors.

Signs & Symptoms

• A new lump or mass in the breast or underarm
• Thickening or swelling of part of the breast
• Irritation, dimpling, or texture changes of the breast skin
• Redness or flaking of the nipple or skin
• Nipple retraction or nipple pain
• Unexpected nipple discharge (sometimes bloody)
• Change in size or shape of the breast

Inflammatory breast cancer is an aggressive form in which cancer cells block lymph vessels in the skin; the breast may look red, feel warm, and become swollen—often without a distinct lump.

Diagnosis & Classification

Diagnosis usually includes a clinical exam, imaging (mammogram, ultrasound, MRI), and a biopsy of any suspicious area. Pathology testing confirms cancer and identifies its biology—hormone receptors (ER/PR), HER2 status, grade, and other features. Staging describes how far the cancer has spread (tumor size, lymph nodes, and distant sites).

Treatment & Prognosis

Treatment is personalized based on stage and tumor biology. Common approaches include:

• Surgery: lumpectomy or mastectomy; sentinel lymph node biopsy or axillary dissection
• Radiation therapy
• Systemic therapy: hormone therapy (for ER/PR-positive disease), chemotherapy, HER2-targeted therapy, and immunotherapy

Many early-stage cancers are curable or controllable long-term. Metastatic breast cancer is usually not curable, but modern treatments can extend survival and improve quality of life.

Why Fight.Cure.Win Matters

Because breast cancer is heterogeneous, education and early detection save lives. Fight.Cure.Win helps patients, caregivers, and communities access clear, trustworthy information and practical support—so together we can fight, accelerate cures, and help more people win.

Sources & Attribution

• National Cancer Institute – cancer.gov/types/breast
• CDC – cdc.gov/breast-cancer/about
• MedlinePlus – medlineplus.gov/breastcancer.html

This content is for educational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare professional.