Breast Cancer — Causes, Stages, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Breast cancer is the most common cancer in women worldwide and the second most common overall, with 2.3 million new diagnoses and 685,000 deaths annually. In developed countries, 1 in 8 women will develop breast cancer in their lifetime. Most breast cancers arise from ductal epithelium — invasive ductal carcinoma (IDC) accounts for 70-80% of cases. Major subtypes include hormone receptor-positive (ER+/PR+) — most common and best prognosis; HER2-positive — more aggressive, responds to anti-HER2 therapy; and triple-negative breast cancer (TNBC) — aggressive, lacks ER, PR, and HER2. Breast cancer survival has improved dramatically over the past three decades — 10-year survival in the UK rose from 43% in the 1970s to 75% in 2020 — reflecting advances in early detection through mammographic screening, surgical techniques, and systemic therapy. Hormone receptor-positive breast cancer (ER+/PR+) accounts for 70-80% of all cases and responds to endocrine therapy. HER2-positive tumours (15-20%) respond to trastuzumab-based regimens. Triple-negative breast cancer (TNBC, 15%) is the most aggressive subtype and lacks targeted hormonal or anti-HER2 treatment options.

Risk factors include female sex (99% of breast cancers occur in women), advancing age (risk doubles every 10 years until menopause), family history of breast or ovarian cancer, BRCA1/BRCA2 mutations (10x higher lifetime risk), dense breast tissue, early menarche, late menopause, nulliparity or first pregnancy after 30, prolonged hormone replacement therapy, obesity (particularly post-menopausal), alcohol consumption, prior chest radiation, and personal history of breast cancer. Only 5-10% of breast cancers are due to inherited BRCA1/2 mutations. Lifetime alcohol consumption of one drink daily increases breast cancer risk by approximately 7-10%. Dense breast tissue (detected on mammography) independently increases breast cancer risk 4-6 fold and reduces mammogram sensitivity. Atypical ductal hyperplasia (ADH) or lobular carcinoma in situ (LCIS) on breast biopsy increases lifetime risk 4-5 fold. Hormone-receptor positive breast cancer risk is increased by combined oral contraceptive and hormone replacement therapy use.

The most common presenting feature is a new painless lump in the breast or axilla (armpit). Most breast lumps are benign (cysts, fibroadenomas, lipomas), but all new lumps require medical assessment. Other warning signs: change in breast size or shape, skin changes (redness, dimpling, peau d'orange texture), nipple changes (inversion, discharge, bleeding), and persistent breast or armpit pain. Inflammatory breast cancer presents as rapidly developing breast redness, warmth, and swelling — can mimic mastitis. Early breast cancer often causes no symptoms — detected by screening mammography before it is palpable. Inflammatory breast cancer — characterised by rapid onset of breast erythema, warmth, oedema, and skin thickening resembling the appearance of an orange peel (peau d'orange) — accounts for 1-5% of all breast cancers and may be misdiagnosed as cellulitis or mastitis; it should be evaluated with biopsy if there is no response to antibiotics within 1-2 weeks.

Triple assessment is the diagnostic gold standard: clinical examination + imaging (mammography and ultrasound) + tissue biopsy (core needle biopsy). Mammography detects 85-90% of breast cancers; ultrasound characterises lesions further. MRI of the breast is used for high-risk screening (BRCA carriers), preoperative staging, and assessing response to neoadjuvant chemotherapy. Core biopsy provides histological diagnosis, receptor status (ER, PR, HER2 by immunohistochemistry and FISH), and Ki-67 (proliferation marker). Staging: CT thorax/abdomen/pelvis and bone scan (or PET-CT) for Stages II-IV. Gene expression profiling (Oncotype DX, Mammaprint) guides chemotherapy decisions in early ER+ cancer. Sentinel lymph node biopsy (SLNB) using blue dye and radioisotope tracer identifies the first draining lymph node(s) in the axilla, avoiding full axillary clearance in node-negative patients and its associated lymphoedema risk. Circulating tumour DNA (ctDNA) in blood is an emerging tool for detecting minimal residual disease and early recurrence after treatment.

Surgery: wide local excision (lumpectomy) + sentinel node biopsy for early cancer; mastectomy for larger/multifocal tumours, BRCA carriers, or patient preference; immediate or delayed reconstruction options. Radiotherapy: whole breast radiotherapy after lumpectomy reduces local recurrence by 50-70%. Systemic therapy: hormone receptor-positive cancer — endocrine therapy (tamoxifen for pre-menopausal; aromatase inhibitors for post-menopausal: letrozole, anastrozole, exemestane) for 5-10 years; CDK4/6 inhibitors (ribociclib, palbociclib, abemaciclib) for metastatic HR+ disease. HER2-positive: trastuzumab (Herceptin) ± pertuzumab; TDM-1, tucatinib for later lines. TNBC: chemotherapy (anthracyclines/taxanes), pembrolizumab immunotherapy, olaparib for BRCA-mutated. Neoadjuvant chemotherapy downstages tumours before surgery. Ovarian function suppression (OFS) with GnRH analogues (goserelin, leuprorelin) combined with aromatase inhibitors improves outcomes in pre-menopausal high-risk ER-positive breast cancer compared to tamoxifen alone. Sacituzumab govitecan (antibody-drug conjugate) and olaparib (PARP inhibitor for BRCA-mutated TNBC) have significantly improved outcomes in metastatic triple-negative breast cancer, which historically had few targeted options. CDK4/6 inhibitors (palbociclib, ribociclib, abemaciclib) added to endocrine therapy reduce mortality in HR-positive metastatic disease.

Untreated breast cancer progresses from localised to locally advanced to metastatic disease — most commonly spreading to bone (pain, fractures), liver (liver failure), lungs (breathlessness), and brain (neurological deficits). Metastatic breast cancer is treatable but not curable, with median survival of 2-3 years (improving with modern therapies). Local untreated disease causes skin ulceration, fungating wounds, and lymphoedema from axillary involvement. Early-stage breast cancer detected at Stage I has 99% 5-year survival; Stage IV survival is approximately 28%. Early detection through screening is life-saving.

Breast cancer screening saves lives: annual mammography from age 40-50 onwards (guidelines vary by country) detects cancers before symptoms develop. Perform monthly breast self-examination and report any changes promptly to a doctor. Maintain healthy weight — obesity increases post-menopausal breast cancer risk by 30-60%. Limit alcohol (risk increases 7-10% per daily drink). Breastfeeding reduces risk (2% per year of breastfeeding). Regular exercise reduces risk by 15-20%. BRCA1/2 mutation carriers should discuss risk-reducing options with a genetics team: enhanced screening, chemoprevention (tamoxifen, raloxifene), or prophylactic mastectomy and salpingo-oophorectomy.

See a GP promptly — and expect a 2-week urgent referral — for: any new lump in the breast or axilla (armpit); change in breast size, shape, or contour; skin changes (dimpling, puckering, peau d'orange/orange-peel texture, persistent redness); nipple changes (new inversion, discharge — especially blood-stained, or rash); or unexplained persistent breast or armpit pain. Do not wait to see whether a lump resolves on its own — most breast lumps are benign, but all new ones must be assessed. Seek urgent (same-day) assessment for: rapidly developing breast redness, warmth, swelling, and skin thickening resembling an inflamed breast — this may be inflammatory breast cancer (not mastitis) if not responding to antibiotics within 1-2 weeks. Women with known BRCA1/2 mutations, family history of breast cancer, or previous chest radiotherapy should be enrolled in enhanced surveillance programmes — discuss with your GP or genetics team.