Definition and epidemiology
Breast cancer is a malignancy originating from the epithelial cells of the breast, most often the terminal duct lobular unit. It is classified histologically into ductal carcinoma in situ (DCIS), invasive ductal carcinoma (most common, ~70-80% of cases), and invasive lobular carcinoma (~10-15%), along with less common subtypes.
- It is the most frequently diagnosed cancer among women globally.
- Lifetime risk in women in the US is approximately 1 in 8.
- Male breast cancer exists but accounts for less than 1% of all cases.
- Median age at diagnosis is in the early 60s, though risk rises steadily after age 40.
- Incidence has increased over recent decades partly due to increased screening, while mortality has declined due to earlier detection and better therapy.
- Painless, firm, immobile mass is the classic presenting sign of breast cancer.
- Invasive ductal carcinoma is the most common histologic subtype.
- BRCA1/2 mutations confer the highest hereditary risk and link to triple-negative and ovarian cancer.
- Peau d'orange and nipple retraction suggest locally advanced or inflammatory disease.
- Triple assessment = clinical exam + imaging + core needle biopsy.
- ER/PR-positive tumors are treated with endocrine therapy; HER2-positive tumors receive anti-HER2 therapy.
- Triple-negative breast cancer lacks ER, PR, and HER2 targets and relies on chemotherapy.
- Sentinel lymph node biopsy stages the axilla in clinically node-negative disease.
Etiology and risk factors
Most cases are sporadic, but a combination of hormonal, genetic, and lifestyle factors contributes to risk.
Genetic
- BRCA1 and BRCA2 mutations confer the highest hereditary risk (lifetime risk up to 70-80%); BRCA1 is also linked to triple-negative subtype and ovarian cancer.
- Other syndromes: Li-Fraumeni (TP53), Cowden (PTEN), Peutz-Jeghers.
- Family history of breast or ovarian cancer in a first-degree relative increases risk.
Hormonal and reproductive
- Early menarche, late menopause (prolonged estrogen exposure).
- Nulliparity or first pregnancy after age 30.
- Prolonged combined hormone replacement therapy or oral contraceptive use (modest increase).
- Lack of breastfeeding.
Other
- Increasing age (strongest overall risk factor).
- Prior chest wall radiation (e.g., for Hodgkin lymphoma).
- Obesity, alcohol use, sedentary lifestyle (postmenopausal risk).
- Dense breast tissue on mammography.
- Prior personal history of breast cancer or atypical hyperplasia.
Pathophysiology
Breast carcinogenesis follows a multistep progression driven by accumulated genetic and epigenetic alterations in ductal or lobular epithelium.
- Normal epithelium progresses through atypical hyperplasia to carcinoma in situ (confined by basement membrane) and then invasive carcinoma (breach of basement membrane with stromal invasion).
- Hormone receptor signaling (estrogen receptor, progesterone receptor) drives proliferation in a majority of tumors.
- HER2/neu (ERBB2) gene amplification drives a more aggressive subtype in about 15-20% of cases, targetable with anti-HER2 therapy.
- Triple-negative breast cancer (ER-, PR-, HER2-negative) lacks these targetable receptors, is more common in BRCA1 carriers and younger patients, and tends to be more aggressive.
- Spread occurs via lymphatics (axillary nodes first, following predictable drainage patterns) and hematogenously to bone, lung, liver, and brain.
- Molecular subtyping (luminal A, luminal B, HER2-enriched, basal-like/triple-negative) guides prognosis and treatment selection.
Clinical features
Many cases are now detected on screening mammography before symptoms develop.
- Painless, firm, irregular, poorly mobile breast mass (most common presenting sign when symptomatic).
- Skin changes: dimpling (peau d'orange), retraction, or ulceration.
- Nipple changes: retraction, discharge (especially bloody), or scaling (consider Paget disease of the nipple).
- Axillary or supraclavicular lymphadenopathy.
- Inflammatory breast cancer: rapid onset of erythema, warmth, edema, and peau d'orange, often mistaken for mastitis; carries poor prognosis.
- Advanced/metastatic disease: bone pain, pathologic fractures, dyspnea, jaundice, or neurologic symptoms depending on metastatic site.
Diagnosis
Diagnosis relies on the triple assessment: clinical examination, imaging, and tissue sampling.
Imaging
- Mammography is the primary screening and initial diagnostic tool; findings suggestive of malignancy include spiculated masses, architectural distortion, and clustered pleomorphic microcalcifications.
- Ultrasound helps characterize masses (solid vs cystic) and guides biopsy, especially useful in dense breasts and younger women.
- MRI is used for high-risk screening (e.g., BRCA carriers), preoperative staging, or evaluating extent of disease.
Tissue diagnosis
- Core needle biopsy is the standard for histologic diagnosis, allowing assessment of receptor status.
- Fine needle aspiration may be used for suspicious lymph nodes.
- Pathology report should include histologic type, grade, ER/PR status, HER2 status, and proliferation index (Ki-67) when relevant.
Staging
- TNM staging incorporates tumor size, nodal involvement, and distant metastasis.
- Sentinel lymph node biopsy is used to stage the axilla in clinically node-negative disease.
- Staging workup for metastases (CT chest/abdomen/pelvis, bone scan) is reserved for locally advanced disease or symptomatic patients, not early-stage asymptomatic cases.
Differential diagnosis
- Fibroadenoma: benign, mobile, well-circumscribed mass, typically in younger women.
- Fibrocystic breast changes: cyclical pain and nodularity related to menstrual cycle.
- Breast cyst: smooth, mobile, often tender; confirmed by ultrasound and may resolve with aspiration.
- Mastitis/breast abscess: erythema, warmth, fever, often associated with lactation; can mimic inflammatory breast cancer if not resolving with antibiotics.
- Phyllodes tumor: rapidly growing mass, can be benign or malignant, distinct from carcinoma on histology.
- Fat necrosis: history of trauma or prior surgery, firm irregular mass that can mimic malignancy on imaging.
Management
Treatment is multidisciplinary and depends on stage, molecular subtype, and patient factors. Guideline bodies (NCCN, ASCO, ESMO) broadly agree on the overall framework, with some variation in specific regimens.
Surgery
- Breast-conserving surgery (lumpectomy) plus radiation is oncologically equivalent to mastectomy for most early-stage disease.
- Mastectomy indicated for large tumors, multicentric disease, contraindications to radiation, or patient preference; may include immediate reconstruction.
- Sentinel lymph node biopsy for axillary staging; axillary dissection reserved for node-positive disease.
Radiation therapy
- Standard after breast-conserving surgery.
- Considered after mastectomy for large tumors, positive margins, or significant nodal involvement.
Systemic therapy (guided by receptor status)
- Hormone receptor-positive (ER/PR+): endocrine therapy (tamoxifen in premenopausal women; aromatase inhibitors in postmenopausal women), often for 5-10 years.
- HER2-positive: anti-HER2 targeted therapy (trastuzumab-based regimens), typically combined with chemotherapy.
- Triple-negative: chemotherapy is the mainstay (no targeted hormonal or HER2 therapy available); immunotherapy may be added in select high-risk cases per evolving guidelines.
- Chemotherapy considered for high-risk node-positive disease, large tumors, or aggressive biology regardless of subtype.
- CDK4/6 inhibitors are used in combination with endocrine therapy for certain hormone receptor-positive advanced or high-risk early disease.
Metastatic disease
- Goal shifts to disease control and quality of life; treatment choice guided by receptor status and prior therapy, including endocrine therapy, targeted agents, and chemotherapy as appropriate.
Screening
- Mammography-based screening recommendations vary by guideline body regarding starting age (40 vs 50) and interval (annual vs biennial); shared decision-making is emphasized, especially for women aged 40-49.
Complications and prognosis
- Prognosis is strongly determined by stage at diagnosis, molecular subtype, and nodal status.
- Early-stage, hormone receptor-positive disease generally has the best prognosis; triple-negative and inflammatory subtypes carry worse outcomes.
- Common metastatic sites: bone (most common), lung, liver, brain.
- Treatment-related complications: lymphedema after axillary dissection, radiation-associated skin and cardiac/pulmonary effects, chemotherapy-induced cardiotoxicity (notably with anthracyclines and trastuzumab), and premature menopause from systemic therapy.
- Long-term survivors require surveillance for local recurrence, contralateral breast cancer, and late treatment effects.
- Overall 5-year survival for localized disease is high (over 90%), dropping substantially with distant metastasis.
Breast cancer risk factors — "MOTHER": Menarche early, Obesity, Terminated pregnancy late/none, Hormone therapy, Estrogen exposure prolonged, Relatives with BRCA/family history.
Practice questions
1. A 58-year-old woman undergoes screening mammography that reveals a spiculated mass with clustered microcalcifications in the upper outer quadrant of the left breast. Core needle biopsy confirms invasive ductal carcinoma. Immunohistochemistry shows ER-positive, PR-positive, and HER2-negative status. Which of the following is the most appropriate component of her systemic adjuvant therapy?
2. A 45-year-old woman presents with a rapidly enlarging, erythematous, warm, and edematous left breast over the past 3 weeks, with diffuse skin thickening resembling an orange peel. She is afebrile and has no response to a course of oral antibiotics. Which of the following is the most likely diagnosis?
3. A 34-year-old woman with a strong family history of breast and ovarian cancer tests positive for a BRCA1 mutation. She has no current breast abnormalities on examination or imaging. Which of the following is the most appropriate next step in her management?
Frequently asked questions
What causes breast cancer?
Breast cancer results from accumulated genetic mutations in breast duct or lobular cells that disrupt normal growth control. Most cases are sporadic, driven by hormonal exposure (estrogen), age, and lifestyle factors, while a smaller proportion arise from inherited mutations such as BRCA1 or BRCA2. No single cause explains all cases; it is a multifactorial disease involving genetic susceptibility and environmental or hormonal exposures over time.
What are the first symptoms of breast cancer?
The earliest sign is often a painless, firm lump in the breast or armpit, frequently found incidentally or on screening mammography before any symptoms occur. Other early signs can include nipple discharge, nipple retraction, or subtle skin changes like dimpling. Many early cancers cause no symptoms at all, which is why routine mammographic screening is important for early detection.
How is breast cancer diagnosed?
Breast cancer is diagnosed using the triple assessment: clinical breast examination, imaging (mammography and/or ultrasound, sometimes MRI), and a core needle biopsy for tissue confirmation. The biopsy also determines hormone receptor and HER2 status, which guide treatment. Staging studies may follow to assess the extent of disease, particularly in locally advanced or symptomatic cases.
Is breast cancer curable?
Yes, early-stage breast cancer is often curable, with five-year survival exceeding 90% when caught before it spreads beyond the breast and nearby lymph nodes. Treatment typically combines surgery with radiation and/or systemic therapy tailored to tumor subtype. Metastatic (stage IV) breast cancer is generally not curable but can often be controlled for years with ongoing treatment.
Fibroadenoma vs breast cancer — what is the difference?
A fibroadenoma is a benign, smooth, mobile breast lump common in younger women, while breast cancer typically presents as a firm, irregular, immobile mass more common in older women. Fibroadenomas do not invade surrounding tissue or metastasize, whereas breast cancer is malignant and can spread to lymph nodes and distant organs. Imaging and biopsy distinguish the two definitively.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: C50
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.