01Core principlesThe concepts and mechanisms needed to understand the subject.
Preventive choices serve people who are currently free of breast cancer but whose future risk is high enough that the burdens of intervention may be proportionate. Surveillance aims for earlier detection; endocrine medication lowers the incidence of susceptible tumours; bilateral mastectomy removes most at-risk tissue. These options do different jobs, so comparing them requires a validated baseline risk and an honest description of residual risk rather than a promise of complete prevention.
Medicine selection depends on menopausal status and competing harms. Tamoxifen blocks oestrogen receptors in breast tissue but increases venous thromboembolism and endometrial pathology risk; anastrozole suppresses peripheral oestrogen synthesis after menopause and can accelerate bone loss and cause musculoskeletal symptoms. Surgery needs genetics counselling, documented risk, breast and reconstructive expertise, psychological support and enough time to revisit the choice without coercion.
Key points
- Risk reduction begins with a verified personal and family history, formal category and genetics input when indicated; no medicine or operation should be offered from an unverified anecdotal percentage.
- NICE offers tamoxifen for five years to premenopausal women at high risk and considers it at moderate risk, unless thromboembolic or endometrial-cancer risk makes it unsuitable.
- NICE offers anastrozole for five years to postmenopausal women at high risk and considers it at moderate risk unless severe osteoporosis is present; bone health is part of selection and monitoring.
- Tamoxifen and anastrozole reduce the incidence of mainly hormone-sensitive breast cancer but do not eliminate risk, replace symptom assessment or remove the need for the agreed surveillance programme.
- Risk-reducing bilateral mastectomy can substantially lower breast-cancer risk but leaves residual tissue and carries permanent effects on sensation, appearance, reconstruction and surgical morbidity.
- Good shared decisions use absolute risk over a stated horizon, likely absolute benefit, adverse effects, alternative surveillance, fertility or menopausal concerns, recovery demands and the patient’s values.
02Mechanisms and patternsImportant relationships and how to distinguish them.
A person at moderate or high formal risk who understands five-year endocrine prevention and has no dominant contraindication may consider a medicine pathway.
A small proportion of people at high risk may prefer bilateral risk-reducing mastectomy after genetics assessment and detailed breast and reconstructive counselling.
VTE, endometrial risk, osteoporosis, menopausal symptoms, fertility plans and interacting medicines can alter the net value of endocrine prevention.
The patient can explain baseline risk, expected benefit, residual risk, alternatives and permanent consequences without feeling pushed by family or clinicians.
03Interpreting evidenceInformation, measurements and their limitations.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Validated risk calculation - Why
- Quantify baseline risk over a stated horizon and establish whether moderate or high-risk prevention guidance applies.
- Interpretation and limitations
- The estimate must reflect verified history and current inputs. Medication benefit should be expressed against this absolute baseline rather than as relative reduction alone.
- 02
Genetics assessment and report - Why
- Clarify whether a pathogenic variant changes organ-specific risk, surveillance, family advice or surgical discussion.
- Interpretation and limitations
- Use the actual report and gene-specific advice. A variant of uncertain significance does not justify risk-reducing mastectomy as if pathogenic.
- 03
Bone-health assessment - Why
- Identify osteoporosis and fracture risk before an aromatase-inhibitor prevention pathway.
- Interpretation and limitations
- NICE defines severe osteoporosis as a DEXA T-score of minus 2.5 standard deviations or lower in this guideline context and advises against anastrozole when severe osteoporosis is present.
- 04
Preoperative breast and reconstructive review - Why
- Confirm no current malignancy and map surgical, reconstructive and anaesthetic implications before preventive mastectomy.
- Interpretation and limitations
- A new symptom or suspicious image becomes a diagnostic problem first. Reconstruction choices are individual and may require staged operations.
04Applied reasoningWorked examples connecting principles to decisions.
01Worked case: premenopausal preventionDecide whether tamoxifen adds valueIllustrative worked example: a healthy premenopausal 39-year-old has a specialist-confirmed 31% lifetime breast-cancer risk, no current breast symptoms and asks about tablets rather than surgery.+
- 1The clinic confirmed no pregnancy, no breastfeeding, no personal VTE or important thromboembolic/endometrial risk, no interacting medication and no planned operation or immobility. Her surveillance plan was current; she accepted non-hormonal contraception and had no QT-risk factors requiring screening ECGs.
- 2The clinician offered five years of tamoxifen under NICE high-risk guidance, explaining reduced breast-cancer incidence, the lack of demonstrated mortality benefit, adverse effects and surveillance alone. After reviewing the available decision aid, she chose medication.
- 3The experienced prescriber initiated tamoxifen 20 mg orally once daily within shared care, documented contraception during treatment and for 9 months after stopping, and gave written VTE, abnormal-bleeding and surgery/immobility advice.
- 4At her six-week review, she reported daily adherence and mild tolerable hot flushes, with no vaginal bleeding, thrombotic symptoms or new medicines. She confirmed continued non-hormonal contraception and preferred to continue treatment.
- 5The team recorded that observed tolerance and renewed the agreed review and surveillance plan. The example demonstrates an informed choice and early safety follow-up, not evidence that six weeks of treatment had prevented a future cancer.
02Postmenopausal medicine pathwayProtect bone while reducing riskA 58-year-old at high risk is postmenopausal, has no prior VTE and wants medication; DEXA does not show severe osteoporosis.+
- 1Confirm menopause, using LH, FSH and/or oestradiol if uncertain; document the actual DEXA value, fracture history, blood pressure/lipid and cardiovascular risks, renal/hepatic context and oestrogen-containing medicines.
- 2Discuss anastrozole as the NICE high-risk option only if severe osteoporosis is absent under CG164's T-score at or below −2.5 definition. Explain that the selected product's different exclusion threshold does not supersede NICE candidate selection; compare absolute benefit, adverse effects and surveillance alone.
- 3If selected, use anastrozole 1 mg orally once daily for five years through an experienced shared-care pathway; avoid concurrent tamoxifen or oestrogen therapy.
- 4Review adherence, arthralgia, bone density and fracture prevention. Investigate new or worsening cardiovascular risk or symptoms and reconsider the medication's benefit-risk balance; continue the agreed breast-surveillance schedule.
03Risk-reducing mastectomy pathwayMake an irreversible choice deliberatelyA BRCA1 carrier prefers the largest available reduction in breast-cancer risk and asks for bilateral mastectomy.+
- 1Confirm the constitutional result, current absence of malignancy and gene-specific risk through the genetics and breast teams.
- 2Discuss risk reduction and residual breast tissue, surgical and anaesthetic complications, sensation loss, sexuality, body image, breastfeeding implications and surveillance alternatives.
- 3Offer reconstructive consultation covering implant and autologous options, immediate or delayed reconstruction, scars, donor-site effects and the possibility of revision surgery.
- 4Provide psychological support and time for more than one consultation; check that the decision reflects the patient’s priorities rather than family pressure.
- 5Before operating, verify informed consent and the agreed pathological examination, postoperative support and plan for remaining gene-associated cancer risks.
05Relevant medicines and safetySpecific regimens and precautions where medicines are relevant.
Tamoxifen
20 mg by mouth once daily for 5 years for primary breast-cancer risk reduction in an appropriately selected moderate- or high-risk adult under an experienced shared-care pathway.Exclude pregnancy before starting; use non-hormonal contraception during treatment and for 9 months after stopping, following the current Tillomed SmPC rather than older NICE timing. Tamoxifen is not recommended during breastfeeding: agree whether nursing or treatment will stop. Do not use with product hypersensitivity or concurrent anastrozole; primary prevention is also contraindicated after DVT/PE or with coumarin anticoagulants. NICE excludes candidates with a history or increased risk of thromboembolic disease or endometrial cancer. Assess other VTE risks and stop approximately 6 weeks before elective surgery; consider interruption during immobility with the prescribing team. New leg swelling, chest pain or breathlessness requires immediate assessment; stop tamoxifen if VTE develops and initiate appropriate treatment. Investigate abnormal vaginal bleeding or other new gynaecological symptoms promptly. Avoid potent CYP2D6 inhibitors where possible, including paroxetine, fluoxetine, bupropion, quinidine and cinacalcet; concurrent oral hormonal contraception or HRT is not recommended. For QT-risk factors, cardiac disease, QT-prolonging medicines or electrolyte disturbance, obtain baseline ECG and electrolytes, correct abnormalities, and repeat ECG at steady state, at least 4 weeks after starting; subsequent checks follow symptoms and changing risks. This is risk-based monitoring, not universal ECG screening. Discuss bone health in premenopausal patients. Withdraw immediately for suspected severe blistering/mucosal skin reactions and never restart after SJS/TEN; seek urgent assessment for angioedema.
Anastrozole
1 mg by mouth once daily for 5 years for primary breast-cancer prevention in an appropriately selected postmenopausal adult under an experienced shared-care pathway.Contraindicated in pregnancy, breastfeeding or product hypersensitivity; do not use before menopause. If menopausal status is uncertain, confirm biochemically with LH, FSH and/or oestradiol before treatment. Avoid concurrent tamoxifen and oestrogen-containing therapy. Mild/moderate renal impairment and mild hepatic disease need no dose change; GFR below 30 mL/min or moderate/severe hepatic impairment requires individual benefit-risk assessment and cautious specialist use, not an invented reduced dose. Apply NICE CG164 prevention selection: do not offer anastrozole with a DEXA T-score at or below −2.5. The selected Milpharm SmPC separately calls T-score below −4.0 or more than two vertebral fractures unsuitable for prevention; this does not relax NICE selection. Assess baseline fracture risk and bone density where indicated, arrange repeated assessment, and start/monitor osteoporosis or osteopenia treatment when appropriate. Assess blood pressure, lipids and cardiovascular history before preventive use. Review new or worsening hypertension, lipid abnormalities or cardiovascular symptoms promptly, considering anastrozole as a contributor and reassessing whether preventive benefit still outweighs harm. Monitor arthralgia, menopausal symptoms and adherence alongside bone health.
06Checking understandingVerify the reasoning, revisit uncertainties and apply feedback.
- During preventive medication, review adherence and vasomotor, gynaecological, thrombotic, musculoskeletal and sexual effects at an interval agreed by the specialist pathway.
- For tamoxifen, agree pregnancy exclusion and non-hormonal contraception through treatment and for 9 months afterwards, surgery/immobility advice and prompt assessment of VTE or abnormal gynaecological symptoms. Use baseline and at-least-4-week ECG/electrolyte checks only when QT risk warrants them, with subsequent risk-based review. Routine endometrial screening is not a substitute for investigating symptoms.
- For anastrozole, record menopausal certainty, baseline fracture/DEXA assessment and a bone-protection plan, with repeated assessment if treatment continues. Review blood pressure, lipid/cardiovascular problems and new symptoms, and reassess benefit-risk if these develop or worsen.
- After risk-reducing mastectomy, monitor wound, flap or implant viability, infection, seroma, pain, shoulder movement and psychological recovery while retaining symptom review for residual tissue.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Relative benefit needs a baseline
The same relative reduction produces different absolute benefit at moderate and very high starting risks, which changes the balance against adverse effects.
Prevention does not diagnose
A person taking tamoxifen or after mastectomy still needs prompt assessment of a new lump, skin change or axillary symptom.
Mastectomy leaves residual risk
Microscopic breast tissue remains in skin flaps and the axillary tail, so the operation greatly reduces risk without making it zero.
Declining is a valid outcome
After balanced counselling, enhanced surveillance may fit the patient’s values better than medication or surgery and should be supported without repeated pressure.
Incidence benefit and the post-mastectomy limit
NICE chemoprevention counselling includes reduced invasive breast-cancer risk and the lack of demonstrated mortality benefit, alongside side effects, surveillance alone and risk-reducing surgery where appropriate. Do not offer chemoprevention after bilateral risk-reducing mastectomy in previously high-risk women; residual tissue does not itself create an indication to add preventive endocrine medication.
08Common pitfallsFrequent interpretation and management errors.
- 01
Offering tamoxifen without asking about previous DVT, pulmonary embolus, pregnancy or anticoagulation can turn preventive treatment into avoidable harm.
- 02
Starting anastrozole in a premenopausal person or someone with severe osteoporosis ignores its physiological requirement and bone consequences.
- 03
Quoting “risk reduced” without absolute numbers, time horizon or residual risk prevents meaningful comparison between medicine, surgery and surveillance.
- 04
Presenting bilateral mastectomy as mandatory after a pathogenic variant undermines informed consent and underestimates permanent reconstructive and sensory consequences.