What is breast cancer?

Breast cancer is a group of diseases in which malignant (cancer) cells form in the tissues of the breast. Most breast cancers begin in the cells of the milk ducts (ductal carcinomas) or the milk-producing lobules (lobular carcinomas). Tumors may be invasive (able to spread to surrounding tissue) or in situ (localized). Advances in molecular biology have shown that "breast cancer" includes many subtypes with different biology, prognosis, and treatment responses.

Types and subtypes

Understanding the type and molecular subtype of breast cancer is crucial for treatment planning.

• Ductal carcinoma in situ (DCIS): Non-invasive cancer confined to the milk ducts. It is highly treatable and often curable with surgery and, in some cases, radiation.
• Invasive ductal carcinoma (IDC): The most common invasive type; begins in ducts and can spread to surrounding tissue and lymph nodes.
• Invasive lobular carcinoma (ILC): Begins in lobules and can be more diffuse in the breast.
• Special histologies: Medullary, mucinous, tubular — less common types with distinct features and often favorable prognosis.

Crucially, tumors are characterized by receptor status which guides systemic therapy:

• Hormone receptor–positive (ER/PR positive): Tumors that express estrogen and/or progesterone receptors often respond to endocrine therapies (tamoxifen, aromatase inhibitors).
• HER2-positive: Tumors overexpressing HER2 (human epidermal growth factor receptor 2) are treated with HER2-targeted therapies (trastuzumab, pertuzumab, other agents).
• Triple-negative breast cancer (TNBC): Lacking ER, PR, and HER2; more aggressive biologically in many cases but sensitive to chemotherapy and increasingly to immunotherapy and targeted drugs in select patients.

Risk factors and prevention

Breast cancer risk is influenced by a combination of non-modifiable and modifiable factors. Risk increases with age; most cases occur in adults over 50, but younger patients can develop breast cancer as well.

Non-modifiable risk factors

• Age (risk rises with age)
• Female sex (though men can develop breast cancer)
• Genetic predisposition: BRCA1/BRCA2 and other inherited mutations significantly increase lifetime risk
• Family history of breast or ovarian cancer
• Previous chest radiation (especially at a young age)
• Personal history of atypical hyperplasia or prior breast cancer

Modifiable risk factors

• Alcohol consumption (dose-dependent relationship)
• Obesity, especially after menopause
• Physical inactivity
• Combined (estrogen–progestin) hormone replacement therapy (long-term use increases risk)
• Reproductive factors: early menarche, late menopause, nulliparity, or late first pregnancy can slightly increase risk

Prevention strategies include maintaining a healthy weight, regular physical activity, limiting alcohol, breastfeeding when possible, and careful discussion of hormone therapy risks and benefits with clinicians. For high-risk individuals (e.g., BRCA mutation carriers), enhanced screening, chemoprevention (tamoxifen, raloxifene), or risk-reducing surgery (prophylactic mastectomy or oophorectomy) may be considered.

Screening and early detection

Early detection improves outcomes. Screening recommendations vary slightly by country and organization, but common elements include:

• Mammography: Standard screening tool with proven mortality benefit in population studies. Routine screening typically begins around age 40–50 depending on guidelines, and continues annually or biennially.
• Clinical breast exam: Performed by healthcare professionals; supplemental but not a replacement for imaging.
• Breast MRI: Recommended for high-risk individuals (e.g., BRCA mutation carriers) because of higher sensitivity.
• Ultrasound: Useful as an adjunct, particularly in dense breast tissue or to evaluate palpable lumps.

Shared decision-making between patients and clinicians is important: screening choices should consider individual risk, benefits, false-positive rates, and patient preferences.

Common signs and symptoms

Early breast cancer may be asymptomatic and found on screening imaging. When symptoms occur, they typically include:

• A new lump or mass in the breast or underarm
• Change in breast size or shape
• Skin changes: dimpling, puckering, redness, or peau d’orange (orange-peel texture)
• Nipple changes: inversion, discharge (particularly bloody), or crusting
• Persistent local pain (though many breast cancers are painless)

Any persistent breast change should prompt evaluation by a clinician and appropriate imaging.

Diagnostic tests and staging

Diagnostic evaluation typically follows a suspicious clinical exam or abnormal screening imaging.

Imaging

• Mammography (diagnostic views)
• Ultrasound (characterizes cystic vs solid lesions)
• Breast MRI (used when additional detail is needed)

Tissue diagnosis

Definitive diagnosis requires biopsy:

• Fine-needle aspiration (FNA) — less commonly used for definitive diagnosis
• Core needle biopsy — standard approach to obtain tissue for histology and receptor testing
• Excisional biopsy — surgical removal of the lesion when necessary

Pathology and receptor testing

Biopsy samples are analyzed for histologic type, tumor grade, and biomarkers including estrogen receptor (ER), progesterone receptor (PR), HER2 status, and proliferation markers (e.g., Ki-67). These results guide systemic therapy decisions.

Staging

Staging uses the TNM system (Tumor size, Nodal involvement, Metastasis) and molecular features. Staging helps predict prognosis and determine the scope of treatment (local vs systemic).

Treatment options

Treatment is individualized based on stage, biology, patient health, and preferences. Most care combines local therapy (surgery ± radiation) with systemic therapy (chemotherapy, endocrine therapy, HER2-targeted therapy, targeted agents, immunotherapy) when indicated.

Surgery (local control)

• Breast-conserving surgery (lumpectomy/partial mastectomy): Removes the tumor with a margin of healthy tissue and is usually followed by radiation to minimize local recurrence.
• Mastectomy: Removal of the entire breast; options include skin-sparing and nipple-sparing techniques in eligible patients.
• Sentinel lymph node biopsy: Minimally invasive method to stage the axilla by removing the first draining lymph node(s).
• Axillary lymph node dissection: Performed when multiple nodes are involved.
• Reconstruction: Immediate or delayed breast reconstruction using implants or autologous tissue is an option for many patients and should be discussed preoperatively.

Radiation therapy (RT)

RT reduces local recurrence after breast-conserving surgery and is frequently used after mastectomy in selected high-risk cases. Techniques include whole-breast irradiation, partial-breast RT, and hypofractionated schedules (shorter overall treatment courses). RT is planned carefully to minimize exposure to heart and lungs.

Systemic therapy

Systemic treatments target micrometastatic disease and reduce recurrence:

• Endocrine (hormone) therapy: For ER/PR-positive disease — options include tamoxifen (pre- and postmenopausal use) and aromatase inhibitors (postmenopausal). Duration is typically 5–10 years depending on risk.
• Chemotherapy: Cytotoxic regimens remain important for many high-risk or triple-negative cancers. Selection depends on tumor biology and stage.
• HER2-targeted therapy: Trastuzumab and other agents dramatically improve outcomes for HER2-positive disease, often combined with chemotherapy.
• Targeted therapies and PARP inhibitors: Used for select molecular subgroups (e.g., BRCA-mutated tumors may respond to PARP inhibitors).
• Immunotherapy: Checkpoint inhibitors show benefit in some triple-negative breast cancers when combined with chemotherapy in advanced or high-risk settings.

Sequence and combination of therapies are tailored in multidisciplinary tumor boards to optimize outcomes and minimize toxicity.

Managing side effects and supportive care

Cancer treatment can cause acute and chronic side effects. Early supportive care improves tolerance and quality of life.

Common treatment-related effects

• Surgical: pain, wound healing issues, lymphedema (arm swelling) after nodal surgery
• Radiation: skin irritation, fatigue, localized fibrosis
• Chemotherapy: nausea, hair loss, neutropenia, neuropathy, fatigue
• Endocrine therapy: hot flashes, joint pain, bone density changes
• Targeted therapy: cardiotoxicity (e.g., trastuzumab monitoring), skin or GI effects

Supportive measures include antiemetics for nausea, growth factors for blood count support, physical therapy and lymphedema management, bone density monitoring and treatment, cardiology surveillance when needed, and integrative support (nutrition, psychosocial support, exercise programs).

Survivorship and follow-up

After initial treatment, long-term follow-up includes:

• Regular clinical visits and annual mammography (or tailored imaging if reconstructed)
• Management of long-term side effects (lymphedema, neuropathy, cognitive changes)
• Cardiovascular and bone-health monitoring for patients who received certain therapies
• Psychosocial support, fertility counseling (if relevant), and vocational rehabilitation

Survivorship care plans—detailing treatments received, potential late effects, and recommended surveillance—help coordinate care between oncology and primary care teams.

Advanced and metastatic breast cancer

When breast cancer spreads beyond the breast and regional nodes (metastatic disease), it becomes a chronic condition for many patients. Treatment focuses on prolonging life, controlling symptoms, and preserving quality of life. Options include hormonal therapies, sequential targeted agents, chemotherapy, bone-directed therapies for skeletal metastases, radiation for symptom control, and palliative care integrated early.

Emerging therapies and research directions

Oncology is rapidly evolving. Key research areas include:

• Precision oncology using genomic profiling to match targeted agents
• Next-generation antibody-drug conjugates (ADCs) for HER2-low and other targets
• Novel immunotherapy combinations for triple-negative disease
• PARP inhibitors and other agents for DNA-repair deficient tumors
• De-escalation trials to reduce overtreatment in low-risk cancers
• Improved strategies for preventing and treating treatment-related toxicities

Frequently asked questions (FAQ)

Resources & next steps

If you or a loved one is facing a possible or confirmed diagnosis of breast cancer, consider these steps:

1. See a breast specialist (breast surgeon or medical oncologist) for prompt evaluation and multidisciplinary planning.
2. Request a copy of your pathology report and ask for clarification of key terms (stage, grade, receptor status).
3. Consider a second opinion for complex cases—many centers offer virtual consultations.
4. Connect with patient support organizations (e.g., local cancer societies, breast cancer foundations) for practical help and peer support.
5. Ask about clinical trials that may be appropriate—these offer access to novel therapies and contribute to research.