Estrogens, Progestins and SERMs

• Oestrogens relieve vasomotor symptoms and preserve bone density, but raise the risk of venous thromboembolism and, when unopposed in a woman with a uterus, of endometrial hyperplasia and carcinoma — which is why a progestin is added whenever the uterus is present.
• Progestins oppose endometrial proliferation, and are the contraceptive mainstay through inhibition of the LH surge, thickening of cervical mucus and endometrial thinning.
• Tamoxifen — antagonist in breast, agonist in endometrium and bone. Hence benefit in oestrogen receptor–positive breast cancer, protection of bone, and an increased risk of endometrial carcinoma and thromboembolism.
• Raloxifene — antagonist in breast and endometrium, agonist in bone. Used for osteoporosis without the endometrial risk, still carrying thromboembolic risk.
• Clomiphene — antagonist at the hypothalamus, blocking oestrogen negative feedback to raise gonadotropins and induce ovulation.
• Aromatase inhibitors (anastrozole, letrozole) block peripheral oestrogen synthesis and are used in postmenopausal breast cancer.

Exogenous hormone exposure (the usual stem)

• Systemic menopausal hormone therapy: oral conjugated equine oestrogen or 17-beta estradiol, with or without a progestin, for vasomotor symptoms.
• Combined hormonal contraceptives: ethinyl estradiol plus a progestin; the oestrogen component carries the thrombotic and hepatic risk.
• SERMs: tamoxifen (adjuvant/risk-reducing), raloxifene (osteoporosis), clomiphene (ovulation induction).
• Aromatase inhibitors: anastrozole, letrozole, exemestane — the mirror-image problem, oestrogen deprivation.

Endogenous hyperoestrogenism (unopposed-oestrogen states)

• Obesity: adipose aromatase converts androstenedione to estrone; the dominant modifiable driver of endometrial carcinoma.
• Chronic anovulation (PCOS): no corpus luteum, therefore no progesterone to oppose proliferation.
• Oestrogen-secreting tumours: granulosa cell tumour (Call-Exner bodies, inhibin B elevation), thecoma.
• Cirrhosis: impaired hepatic oestrogen clearance and raised SHBG — gynaecomastia, spider angiomata, palmar erythema in a man.

Modifiable risk factors examiners plant

• Smoking, especially ≥15 cigarettes/day at age ≥35 — a CDC US Medical Eligibility Criteria category 4 (absolute) contraindication to combined hormonal contraception because of arterial thrombotic risk.
• Obesity, immobility, recent surgery, uncontrolled hypertension, hypertriglyceridaemia.
• Oral rather than transdermal route — first-pass hepatic exposure is what drives clotting-factor synthesis.

Non-modifiable risk factors

• Inherited thrombophilia, above all factor V Leiden, which multiplies rather than adds to oestrogen-associated VTE risk; also prothrombin G20210A, protein C/S and antithrombin deficiency.
• Prior VTE, stroke, or MI; known or suspected oestrogen-receptor-positive breast cancer; unexplained vaginal bleeding; active liver disease; pregnancy.
• Migraine with aura — stroke risk; category 4 for combined contraceptives per CDC US MEC.
• Increasing age, nulliparity, late menopause, early menarche, Lynch syndrome for endometrial carcinoma; postmenopausal status specifically amplifies tamoxifen's endometrial risk.

• Receptor biology: oestrogen receptors alpha and beta are nuclear hormone receptors. Ligand binding displaces heat-shock proteins, permits dimerisation and binding to oestrogen response elements, and recruits coactivators to drive transcription. The progesterone receptor is itself an oestrogen-induced gene — which is why PR positivity in breast cancer implies an intact, functional ER pathway.
• Why a SERM is agonist in one tissue and antagonist in another: the ligand-bound receptor adopts a conformation that determines whether coactivators or corepressors dock. Tissues differ in their coactivator/corepressor ratio and in ER-alpha versus ER-beta content, so the same drug transcribes in endometrium and bone while silencing in breast. This single concept generates every tamoxifen adverse effect.
• Endometrium: unopposed oestrogen drives glandular mitosis without the secretory, antimitotic, apoptosis-promoting counterweight of progesterone. Persistent proliferation → simple hyperplasia → hyperplasia with atypia → endometrioid (type I) carcinoma. Progestins downregulate ER and induce 17-beta-hydroxysteroid dehydrogenase, terminating the loop.
• Liver and thrombosis: oral oestrogen undergoes first-pass hepatic exposure and increases synthesis of factors II, VII, IX, X and fibrinogen while reducing protein S and antithrombin activity — an acquired activated protein C resistance. Transdermal delivery bypasses the portal circulation and is associated with less of this effect.
• Bone: oestrogen suppresses osteoblast RANKL and promotes osteoclast apoptosis. Withdrawal at menopause unleashes high-turnover resorption, hence trabecular-predominant loss at spine and hip. Tamoxifen and raloxifene reproduce the protective signal; aromatase inhibitors abolish it, accelerating loss.
• Hypothalamus: oestrogen loss narrows the thermoneutral zone of the preoptic thermoregulatory centre, so trivial core-temperature shifts trigger flushing and sweating. Clomiphene exploits the same axis in reverse — blocking hypothalamic ER removes negative feedback, raising GnRH pulse frequency, FSH and LH, and recruiting a follicle.
• Binding proteins: oestrogen raises SHBG, TBG and cortisol-binding globulin, so total thyroxine rises with a normal free T4 and TSH.

Oestrogen deficiency (the menopausal stem — woman around age 51, 12 months of amenorrhoea)

• Vasomotor symptoms: sudden flushing of face and chest, drenching night sweats, sleep fragmentation — narrowed hypothalamic thermoneutral zone.
• Genitourinary syndrome of menopause: vaginal dryness, dyspareunia, urinary urgency; exam shows pale, thin, poorly rugated mucosa with loss of elasticity.
• Bone loss: silent until a fragility fracture — vertebral compression with height loss and kyphosis, or a distal radius (Colles) fracture after a low-energy fall.

Oestrogen excess / unopposed oestrogen

• Abnormal uterine bleeding, and in the postmenopausal woman any bleeding at all — the presentation of hyperplasia or carcinoma until proven otherwise.
• Breast tenderness, endometrial thickening; in men, gynaecomastia.

Drug-specific presentations examiners favour

• Tamoxifen: a premenopausal or postmenopausal woman on adjuvant therapy for ER-positive breast cancer with hot flushes (antagonist effect), new vaginal bleeding (endometrial agonist), or unilateral leg swelling and pleuritic chest pain (VTE). Cataracts and retinopathy occur with prolonged use.
• Raloxifene: hot flushes and leg cramps, plus VTE risk — but no endometrial stimulation, so postmenopausal bleeding on raloxifene points elsewhere.
• Aromatase inhibitors: postmenopausal woman with symmetric arthralgia and morning stiffness, vaginal dryness, and accelerated bone loss on DXA.
• Clomiphene: infertility stem with visual scotomata/blurring, ovarian enlargement, multiple gestation, or ovarian hyperstimulation syndrome (abdominal distension, ascites, dyspnoea, haemoconcentration).
• Combined contraceptives: nausea, breakthrough bleeding, breast tenderness, melasma (chloasma), hypertension, and rarely right upper quadrant pain from a hepatic adenoma.
• Progestin-only/depot medroxyprogesterone: irregular spotting then amenorrhoea, weight gain, mood change, reversible bone mineral density decline. Drospirenone-containing pills may present with hyperkalaemia given its antimineralocorticoid activity.

Menopause

• Clinical diagnosis: 12 consecutive months of amenorrhoea at the expected age. ACOG does not require hormonal testing. An elevated FSH with low estradiol supports the diagnosis and is needed mainly when premature ovarian insufficiency (age <40) is suspected — in which case check karyotype and FMR1 premutation.
• Exclude pregnancy with a urine or serum hCG before starting any hormonal therapy.

Postmenopausal bleeding — the mandatory workup

• Initial test: transvaginal ultrasound. Per ACOG, an endometrial stripe ≤4 mm in a postmenopausal woman with bleeding has a very high negative predictive value; a stripe >4 mm, or persistent/recurrent bleeding regardless of thickness, requires tissue.
• Confirmatory/gold standard: endometrial biopsy; hysteroscopy with dilation and curettage if the biopsy is non-diagnostic or bleeding persists. Findings range from hyperplasia without atypia to atypical hyperplasia/endometrial intraepithelial neoplasia to endometrioid adenocarcinoma.
• In tamoxifen users, subendometrial cystic change makes the stripe measurement unreliable — proceed to biopsy/hysteroscopy for bleeding. ACOG recommends against routine endometrial surveillance in asymptomatic tamoxifen users.

Osteoporosis

• DXA of hip and lumbar spine; WHO criteria — T-score ≤ -2.5 is osteoporosis, -1.0 to -2.5 osteopenia. FRAX estimates 10-year fracture probability and guides treatment in the osteopenic range. USPSTF recommends screening women ≥65 and younger postmenopausal women at increased risk.

Suspected VTE on oestrogen

• Risk-stratify with the Wells score; D-dimer to exclude in low/intermediate probability; compression ultrasound for DVT and CT pulmonary angiography for PE. Thrombophilia testing does not change acute management and is deferred.

Before endocrine therapy for breast cancer

• ER, PR and HER2 immunohistochemistry on tumour tissue determines eligibility; menopausal status (FSH/estradiol if ambiguous) determines tamoxifen versus aromatase inhibitor.

Vasomotor symptoms of menopause

• First-line, if not contraindicated: systemic oestrogen (17-beta estradiol) — the most effective therapy per The Menopause Society and ACOG. Add a progestin (micronised progesterone or a levonorgestrel IUD) in any woman with a uterus; oestrogen alone is acceptable only after hysterectomy.
• Route matters: transdermal estradiol avoids first-pass hepatic clotting-factor induction and is preferred with VTE risk factors, hypertriglyceridaemia or gallbladder disease.
• Timing hypothesis: benefit-risk is most favourable when started before age 60 or within 10 years of menopause; use the lowest effective dose for the shortest reasonable time.
• Non-hormonal options: SSRIs/SNRIs (venlafaxine, escitalopram; low-dose paroxetine is FDA-approved for vasomotor symptoms), gabapentin, clonidine, and a neurokinin-3 receptor antagonist (fezolinetant). Avoid paroxetine and other strong CYP2D6 inhibitors in women on tamoxifen — they block conversion to the active metabolite endoxifen.
• Genitourinary syndrome alone: low-dose vaginal oestrogen, which has minimal systemic absorption and generally does not require a progestin.

Osteoporosis

• First-line: bisphosphonate (alendronate) per the Endocrine Society and ACP. Raloxifene is an alternative in a postmenopausal woman who also wants breast cancer risk reduction and has no thrombotic history. Hormone therapy is not recommended solely for bone protection.

Breast cancer, ER-positive

• Premenopausal: tamoxifen, typically for 5–10 years, with ovarian function suppression added in higher-risk disease (NCCN).
• Postmenopausal: an aromatase inhibitor (anastrozole, letrozole, exemestane) — ineffective premenopausally because ovarian aromatase output is not suppressed and reflex gonadotropin rise stimulates the ovary. Supplement calcium/vitamin D and monitor DXA.
• Risk reduction: USPSTF recommends offering tamoxifen, raloxifene or an aromatase inhibitor to women at increased risk without contraindications.

Emergencies

• Venous thromboembolism / pulmonary embolism: hepatic induction of procoagulant factors with reduced protein S and antithrombin. Unilateral leg swelling, or pleuritic pain with dyspnoea, hypoxia and sinus tachycardia. Risk is shared by oestrogen, tamoxifen and raloxifene — stop the drug and anticoagulate.
• Ischaemic stroke and myocardial infarction: arterial events, amplified by smoking at age ≥35 and by migraine with aura; raloxifene carries a boxed warning for fatal stroke in women with coronary risk.
• Ruptured hepatic adenoma: oral contraceptive-associated; sudden RUQ pain with haemoperitoneum and hypotension.
• Ovarian hyperstimulation syndrome after clomiphene/gonadotropins: VEGF-driven capillary leak with ascites, pleural effusion, haemoconcentration, oliguria and thrombosis.
• Hypertriglyceridaemia-induced pancreatitis from oral oestrogen raising hepatic VLDL output.

Non-emergent but heavily tested

• Endometrial hyperplasia and carcinoma: unopposed oestrogen or tamoxifen's endometrial agonism; signalled by postmenopausal bleeding. Rarely uterine sarcoma. Prevented by concurrent progestin (not applicable to tamoxifen therapy itself).
• Aromatase inhibitor toxicity: oestrogen deprivation → arthralgia/myalgia, accelerated bone loss, osteoporotic fracture, vaginal dryness, dyslipidaemia.
• Tamoxifen ocular toxicity: cataracts, retinopathy; also hepatic steatosis.
• Cholestasis and gallstones: oestrogen increases biliary cholesterol saturation and reduces bile flow.
• Hypertension with combined contraceptives via angiotensinogen synthesis.
• Depot medroxyprogesterone: reversible bone mineral density loss from hypo-oestrogenism; delayed return of fertility.
• Drospirenone: antimineralocorticoid activity → hyperkalaemia, particularly with ACE inhibitors, ARBs or renal impairment.
• Melasma, breakthrough bleeding, and — with clomiphene — multiple gestation.
• Vaginal clear cell adenocarcinoma and Müllerian anomalies in the daughter of a woman given diethylstilbestrol: the classic transplacental oestrogen complication.

• Tamoxifen = breast antagonist, endometrium and bone agonist. Raloxifene = antagonist in breast and endometrium, agonist in bone. Any stem with new vaginal bleeding on endocrine therapy is pointing at tamoxifen, not raloxifene.
• Postmenopausal bleeding on tamoxifen: the single best next step is endometrial biopsy. Transvaginal ultrasound is unreliable here because of subendometrial cystic change, and ACOG advises against routine screening of asymptomatic users.
• Uterus present → add a progestin. Oestrogen alone is only for the woman who has had a hysterectomy; this is the entire mechanism behind oestrogen-driven endometrial carcinoma.
• Aromatase inhibitors are for postmenopausal women only. In a premenopausal woman, ovarian aromatase and reflex gonadotropin rise defeat the drug — that is the classic distractor.
• Do not co-prescribe paroxetine (or other strong CYP2D6 inhibitors) with tamoxifen; tamoxifen is a prodrug requiring CYP2D6 conversion to endoxifen. Choose venlafaxine for hot flushes instead.
• Every oestrogenic agent in this family — oestrogen, tamoxifen, raloxifene — raises VTE risk. Factor V Leiden in the family history is the planted clue; transdermal estradiol is the risk-mitigating route because it bypasses first-pass hepatic clotting-factor synthesis.
• Clomiphene blocks hypothalamic oestrogen receptors, removing negative feedback to raise FSH/LH; expect visual disturbance and multiple gestation. Letrozole is now first-line for ovulation induction in PCOS (ACOG/ASRM).
• Oestrogen raises TBG: total T4 rises, free T4 and TSH stay normal in a euthyroid woman — but a hypothyroid woman on levothyroxine will need a dose increase.
• Common distractor: attributing hot flushes to raloxifene's endometrial effect, or treating a new LBBB-style "rule" as a shortcut — here the shortcut to reject is assuming an ultrasound stripe measurement can substitute for biopsy in a tamoxifen user.