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Cutting off the hormones that breast and prostate cancers feed on has kept people alive for decades. The therapy is now moving from blocking the hormone to destroying its receptor, and from waiting for a scan to switching drugs when a blood test sees resistance coming.
Endocrine therapy is the oldest targeted treatment in oncology: removal of the ovaries for breast cancer in 1896 and castration for prostate cancer in 1941 predate every drug. Tamoxifen (1977) made it a pill, aromatase inhibitors and GnRH analogues refined it, and for two decades the field advanced by combination: CDK4/6 inhibitors with endocrine therapy in breast cancer, and abiraterone, enzalutamide and docetaxel layered onto androgen deprivation in prostate cancer, each adding survival in randomised trials.
The current generation attacks resistance directly. Oral oestrogen-receptor degraders (elacestrant 2023, imlunestrant 2025, camizestrant 2026) and the first approved PROTAC (vepdegestrant 2026) remove the receptor rather than block it and work in tumours with ESR1 mutations; SERENA-6 was the first trial to change treatment on a blood test rather than a scan. PI3K, AKT and mTOR inhibitors address the parallel escape route. In prostate cancer, PARP inhibitors and AKT inhibitors are being matched to the tumours whose biology predicts benefit, and PSMA radioligands are moving earlier.
The pace is set by resistance biology, by the cost of multi-year combination therapy, and by tolerability: the side-effects that make people stop a drug they should take for five or ten years.
Beatson removed the ovaries of a woman with advanced breast cancer in 1896 and watched the tumour regress; Huggins showed in 1941 that castration controlled metastatic prostate cancer. Tamoxifen (1977), a receptor blocker taken as a pill, halved recurrence after breast surgery and became the first targeted cancer drug. GnRH analogues made castration reversible and chemical.
Aromatase inhibitors stopped oestrogen production in postmenopausal women and edged out tamoxifen in adjuvant trials; fulvestrant destroyed the receptor by injection. SOFT and TEXT showed that suppressing the ovaries and adding an aromatase inhibitor prevents more recurrences in young women than tamoxifen alone. Five to ten years of daily therapy became the norm, and adherence and side-effects became the limiting factor.
Abiraterone and enzalutamide, then apalutamide and darolutamide, blocked the androgen pathway inside the tumour after castration stopped working, and were then moved to first metastatic diagnosis (LATITUDE, ARCHES). CHAARTED and STAMPEDE added docetaxel; ARASENS and PEACE-1 proved triplet therapy. EMBARK treated rising PSA after local therapy, and relugolix made testosterone suppression an oral pill. PSMAfore moved the PSMA radioligand ahead of chemotherapy.
Palbociclib (2015), ribociclib and abemaciclib roughly doubled progression-free time when added to endocrine therapy, and ribociclib extended survival (MONALEESA-2). monarchE and NATALEE brought the class into the adjuvant setting; PALLAS and PENELOPE-B showed it does not work for every drug. Alpelisib (SOLAR-1), capivasertib (CAPItello-291), inavolisib and gedatolisib target the PI3K-AKT-mTOR escape pathway in tumours that carry the mutations, at the cost of high blood sugar and rash.
ESR1 mutations let the receptor work without oestrogen, defeating aromatase inhibitors. Oral degraders remove the receptor itself: elacestrant (2023, EMERALD), imlunestrant (2025, EMBER-3) and camizestrant (September 2026). Vepdegestrant, approved in 2026 after VERITAC-2, is the first PROTAC in any disease. SERENA-6 changed the rules of engagement: it switched to camizestrant when an ESR1 mutation appeared in blood, before the scan showed progression, and delayed progression by doing so. FES PET shows which deposits still carry the receptor.
lidERA is the first oral degrader to reduce recurrence after surgery; CAMBRIA-1 and CAMBRIA-2 test whether degraders should replace today's adjuvant pills outright, while persevERA showed they do not automatically win first-line. postMONARCH and evERA map what to do after CDK4/6 failure. Atirmociclib blocks CDK4 only, to keep the benefit without the low blood counts. In prostate cancer, PARP inhibitors (PROpel, TALAPRO-2, MAGNITUDE) work in tumours with DNA-repair defects, capivasertib in PTEN-deficient disease (CAPItello-281), and the EZH2 inhibitor mevrometostat aims to re-sensitise tumours to enzalutamide (MEVPRO-1).
If resistance can be anticipated from blood, therapy could be sequenced or given intermittently to keep the sensitive clone dominant, an approach being tested in lung cancer and proposed for hormone-driven disease. The Breast Cancer Index already asks who benefits from extending therapy beyond five years. The bigger gains may be in staying on treatment: acupuncture for hot flushes and joint pain, cardiometabolic screening for men on long-term androgen deprivation, and low-dose tamoxifen for prevention prescribed outside the oncology clinic.
Every hormonal agent eventually meets resistance, and the biology of the next escape (ESR1, PI3K, AR splice variants) decides which drug comes next. Multi-year combination therapy is priced per month, so cost compounds; shorter-course and de-escalation trials exist only when public funders run them. And the side-effects that make people stop a drug they should take for years are still measured less carefully than the effects on the tumour.
Every era's records, trial outcomes and papers, and every watch item, as JSON.
Probability ranges are named estimates that the claim is borne out on roughly a five-year horizon. They are meant to be argued with: propose a revision with your name and reasoning via a pull request to src/data/confidence.ts.
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Shares CAMBRIA-1 & CAMBRIA-2, postMONARCH, evERA, Gedatolisib.
Shares lidERA, Low-dose tamoxifen for high-risk women, prescribed by pharmacists and nurses, evERA, VERITAC-2.
Shares lidERA, CAMBRIA-1 & CAMBRIA-2, PALLAS & PENELOPE-B, NATALEE.
Shares PEACE-1, CAPItello-281, ARASENS, ARCHES.
Shares FOURLIGHT-1, postMONARCH, MONARCH 3, PALLAS & PENELOPE-B.
Shares Imlunestrant, Inavolisib, Camizestrant, Alpelisib.
Shares EMERALD, EMBER-3, Imlunestrant, Vepdegestrant.