Goserelin

A synthetic decapeptide GnRH superagonist delivered as a biodegradable subcutaneous implant, FDA-approved since 1989 as Zoladex for prostate cancer, advanced breast cancer in premenopausal women, endometriosis, and endometrial thinning before ablation.

Also referenced as: Zoladex, Goserelin Acetate, Goserelin Implant, ICI 118630, ICI-118630, LY01005, Baituowei

Also appears in: Other

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What is Goserelin?

Goserelin is a synthetic decapeptide analog of gonadotropin-releasing hormone with the sequence pyro-Glu-His-Trp-Ser-Tyr-D-Ser(tBu)-Leu-Arg-Pro-Azgly-NH2 and a molecular weight of 1,269 daltons as the free base. It differs from native GnRH at two positions: a tert-butyl-protected D-serine replaces glycine at position 6, and an azaglycine amide replaces the C-terminal glycinamide at position 10. Both changes came out of the ICI (later Zeneca, then AstraZeneca) peptide program in the late 1970s under the code ICI 118630, and both serve the same purpose as the substitutions in leuprolide and triptorelin: resistance to enzymatic cleavage and far higher potency at the pituitary GnRH receptor.

What sets goserelin apart from the other GnRH agonists is the delivery system rather than the pharmacology. It has only ever been marketed as a solid rod of lactide-glycolide copolymer with the peptide dispersed through it, placed under the skin of the abdominal wall with a wide-bore needle, and FDA approved that implant (Zoladex) on December 29, 1989 as a new molecular entity for palliative treatment of advanced prostate cancer. There is no daily injection and no reconstituted vial, and it is effectively absent from research-peptide catalogs. It matters because it is one of the most widely prescribed therapeutic peptides in oncology and gynecology, not because anyone is selling it as a research compound.

How it works

• GnRH receptor superagonism from two substitutions — the position-6 D-amino acid stabilizes the bioactive conformation and blocks the main site of enzymatic cleavage, while the azaglycine at position 10 protects the C-terminus; the ICI chemists reported that the azaglycine series gave some of the most potent LH-releasing analogs then known (Dutta et al., Biochemical and Biophysical Research Communications, 1978, 81(2):382–390; Dutta et al., Journal of Medicinal Chemistry, 1978, 21(10):1018–1024). The resulting analog was active against estrogen-receptor-positive DMBA-induced rat mammary tumors in the first preclinical reports (Nicholson & Maynard, British Journal of Cancer, 1979, 39(3):268–273)
• Stimulation first, then suppression — like every GnRH agonist, goserelin raises LH and FSH after the first dose and only suppresses them under continuous exposure. In men, serum testosterone rises initially and then falls to castrate-range levels about two to four weeks after the first implant; in women, estradiol falls to postmenopausal levels within three weeks and LH and FSH are suppressed to follicular-phase levels within four weeks, though the label notes isolated estradiol elevations in about 10% of women after suppression and failure to suppress by day 28 in 5% or fewer after a single implant (Zoladex 3.6 mg labeling, section 12.2; Furr & Woodburn, Journal of Endocrinological Investigation, 1988, 11(7):535–557)
• The implant supplies the continuous exposure the mechanism requires — the 3.6 mg rod releases drug slowly for roughly the first eight days and then more rapidly and continuously for the rest of the 28-day period; peak plasma concentrations arrive at 12 to 15 days in men and 8 to 22 days in women, and the 10.8 mg rod extends release to 12 weeks (Zoladex labeling, section 12.3). The commonly quoted average release rate of about 120 micrograms per day over the four weeks comes from the pharmacology literature rather than the label (Chrisp & Goa, Drugs, 1991, 41(2):254–288)
• Therapeutic effect is downstream sex-steroid deprivation, not direct action on the tumor — the label describes goserelin as inhibiting pituitary gonadotropin secretion; prostate cancer, hormone-receptor-positive breast cancer, and endometriotic tissue respond because the androgens or estrogens that sustain them are withdrawn. That is why its prostate-cancer trials measured outcomes against orchiectomy and its breast-cancer trials against surgical oophorectomy (Taylor et al., Journal of Clinical Oncology, 1998, 16(3):994–999)

Research status

Goserelin has more than three decades of Phase 3 evidence, including several of the trials that defined modern practice in two cancers, plus a well-documented negative subgroup and a trial that was stopped early for slow accrual.

Approved indications and their regulatory history. Drugs@FDA records the original approval of the 3.6 mg implant on December 29, 1989 (NDA 019726) for palliative treatment of advanced prostate cancer. Indications were added through an efficacy supplement approved February 2, 1993, a separate new-indication application for the 3.6 mg implant approved December 18, 1995 (NDA 020515), and further efficacy supplements approved in June 1997, April 1998, and July 1998; the July 27, 1998 approval was granted the same day to the 10.8 mg application, consistent with the combination indication that both strengths now carry. The 10.8 mg implant itself was approved January 11, 1996 (NDA 020578) as a new dosage form. Current labeling for the 3.6 mg implant covers five uses: combination with flutamide for locally confined Stage T2b–T4 (B2–C) prostate cancer starting eight weeks before and continuing through radiation; palliative treatment of advanced prostate cancer; management of endometriosis including pain relief and lesion reduction, with a recommended course of six months; endometrial thinning before ablation for dysfunctional uterine bleeding; and palliative treatment of advanced breast cancer in pre- and perimenopausal women. The 10.8 mg implant is approved only for the two prostate indications; its label states it is not indicated in women because the data are insufficient to support reliable estradiol suppression. The most recent labeling changes were a September 2025 supplement that added a warning for severe cutaneous adverse reactions and a revision dated March 2026 (approved as a labeling supplement in May 2026); neither added an indication, and as of October 2026 no generic goserelin implant has been approved in the U.S. — Drugs@FDA lists only the three TerSera applications (the original 3.6 mg NDA, the 1995 new-indication NDA for the 3.6 mg implant, and the 10.8 mg NDA).

Prostate cancer. Two cooperative-group trials from the late 1980s established goserelin as the agonist paired with radiotherapy. EORTC 22863 randomized 415 men with locally advanced disease to external irradiation alone or irradiation plus goserelin 3.6 mg every four weeks for three years, with one month of cyproterone acetate to blunt the initial testosterone rise; at a median of 45 months, five-year overall survival was 79% with combined treatment versus 62% with radiotherapy alone (P = 0.001), and disease-free survival among survivors 85% versus 48% (Bolla et al., New England Journal of Medicine, 1997, 337(5):295–300). The long-term report confirmed the survival advantage (Bolla et al., Lancet, 2002, 360(9327):103–106). RTOG 85-31 randomized 977 men to definitive radiotherapy with or without adjuvant goserelin; at five years local control was 84% versus 71% and disease-free survival 60% versus 44%, but overall survival (75% versus 71%, P = 0.52) differed significantly only in the Gleason 8–10 subgroup at that follow-up (Pilepich et al., Journal of Clinical Oncology, 1997, 15(3):1013–1021). The labeled Stage B2–C indication rests on a 466-patient trial in which goserelin plus flutamide plus radiation, against radiation alone, reduced four-year local failure from 33% to 16% and extended median disease-free survival from 2.6 to 4.4 years; the reduction in distant metastases (36% to 27%) was a trend, P = 0.058 (Zoladex 3.6 mg labeling, section 14.1). The two strengths were compared directly in 160 men with advanced prostate cancer, with similar testosterone suppression and three-month PSA declines of 94% with the 10.8 mg implant and 92.5% with three 3.6 mg implants (Zoladex 10.8 mg labeling, section 14.2).

Breast cancer: the goserelin-specific trials. Goserelin’s breast-cancer record is its own, and it predates the SOFT and TEXT trials that most current guidelines cite — those used triptorelin as the protocol-specified agonist (Francis et al., New England Journal of Medicine, 2018, 379(2):122–137), so their results are class evidence rather than goserelin evidence. The intergroup metastatic trial randomized 136 eligible premenopausal women with receptor-positive metastatic disease to goserelin or surgical ovariectomy; failure-free and overall survival were similar (death hazard ratio 0.80, 95% CI 0.53–1.20), but the trial closed early for slow accrual with only 60% power, and the authors could rule out a moderate advantage for surgery rather than demonstrate equivalence. Hot flashes (75% versus 46%) and tumor flare (16% versus 3%) were more common with goserelin (Taylor et al., Journal of Clinical Oncology, 1998, 16(3):994–999). ZEBRA randomized 1,640 premenopausal women with node-positive early breast cancer to two years of goserelin or six cycles of CMF chemotherapy. The result turned on receptor status: in the roughly 74% with estrogen-receptor-positive tumors, goserelin was equivalent to CMF for disease-free survival (hazard ratio 1.01, 95% CI 0.84–1.20), while in ER-negative tumors it was clearly inferior (hazard ratio 1.76, 95% CI 1.27–2.44). Amenorrhea was reversible with goserelin and largely permanent after CMF (22.6% versus 76.9% amenorrheic at three years) (Jonat et al., Journal of Clinical Oncology, 2002, 20(24):4628–4635); the survival update at 7.3 years held the same pattern (Kaufmann et al., European Journal of Cancer, 2003, 39(12):1711–1717). ZIPP pooled four randomized trials under a core protocol, 2,710 women in all, testing two years of goserelin with or without tamoxifen after primary therapy; at a median of 5.5 years goserelin improved event-free survival (hazard ratio 0.80, 95% CI 0.69–0.92) and overall survival (hazard ratio 0.81, 95% CI 0.67–0.99) (Baum et al., European Journal of Cancer, 2006, 42(7):895–904). The 12-year follow-up found two years of goserelin as effective as two years of tamoxifen, with a large benefit in women not taking tamoxifen (13.9 fewer events per 100 women at 15 years) and only a marginal, non-significant addition in women who did (Hackshaw et al., Journal of the National Cancer Institute, 2009, 101(5):341–349).

Ovarian protection during chemotherapy. POEMS/SWOG S0230 (NCT00068601) randomized 257 premenopausal women with hormone-receptor-negative operable breast cancer to chemotherapy with or without goserelin. Among the 135 with complete primary-endpoint data, ovarian failure at two years was 8% with goserelin versus 22% without (odds ratio 0.30, 95% CI 0.09–0.97; P = 0.04); pregnancy occurred in 21% versus 11% of the 218 evaluable women. The authors stated that missing data weaken interpretation (Moore et al., New England Journal of Medicine, 2015, 372(10):923–932). The final analysis reported a five-year cumulative pregnancy incidence of 23.1% versus 12.2% with no adverse effect on disease outcomes; the disease-free and overall survival differences were not statistically significant (Moore et al., Journal of the National Cancer Institute, 2019, 111(2):210–213). An individual-patient meta-analysis of 873 women from five trials, not all using goserelin, put premature ovarian insufficiency at 14.1% with a GnRH agonist versus 30.9% without (Lambertini et al., Journal of Clinical Oncology, 2018, 36(19):1981–1990). The population was receptor-negative by design, so these data do not establish the strategy in receptor-positive disease.

Endometriosis and gynecology. The Zoladex Endometriosis Study Group randomized 315 women to goserelin or danazol 400 mg twice daily for 24 weeks; the revised AFS endometriosis score fell 53% with goserelin versus 33% with danazol, hypoestrogenic effects were more frequent with goserelin, and mean bone mineral density fell 5.4% from baseline with goserelin while rising 1.0% with danazol (Rock et al., Obstetrics & Gynecology, 1993, 82(2):198–205). The label’s own pooled figure, reported under adverse reactions (section 6.8), is a 4.3% average loss of vertebral trabecular bone density after six months in 109 women, with losses of 2.4% and 2.5% relative to pretreatment still present at six and twelve months after stopping — wording the label describes as suggesting “a possibility of partial reversibility.” The endometrial-thinning indication rests on a 358-woman placebo-controlled trial (median endometrial thickness 1.50 mm versus 3.55 mm; amenorrhea six months after surgery 40% versus 26%) (Zoladex 3.6 mg labeling, section 14.4).

Newer formulations. A sustained-release goserelin microsphere injection (LY01005) was approved in China in June 2023 after Phase 3 comparisons against Zoladex in prostate cancer (NCT04563936, 290 enrolled) and breast cancer (NCT05110170, 188 enrolled), both listed as completed. Its developer has described a 505(b)(2) U.S. pathway, but no U.S. application for it has been approved as of October 2026.

Trial registry picture. ClinicalTrials.gov lists 417 studies naming goserelin as an intervention (October 2026), including 126 Phase 3 and 24 Phase 4 records: roughly 218 in prostate cancer, 154 in breast cancer, and 10 in endometriosis. Goserelin now appears mostly as the background androgen- or ovarian-suppression arm of trials testing other drugs — PARP inhibitors, CDK4/6 inhibitors, oral SERDs, and radiotherapy duration — rather than as the agent under study.

Common dosage forms

• 3.6 mg subcutaneous implant (28-day) — a white to cream cylinder about 1 mm in diameter weighing 18 mg, containing 3.8 mg goserelin acetate (3.6 mg goserelin base) dispersed in a biodegradable D,L-lactic and glycolic acid copolymer, preloaded in a single-use syringe with a 16-gauge, 36 mm needle and a protective sleeve; placed in the anterior abdominal wall
• 10.8 mg subcutaneous implant (12-week) — a larger cylinder about 1.5 mm in diameter weighing 36 mg, containing 11.3 mg goserelin acetate, preloaded with a 14-gauge needle; approved for the prostate-cancer indications only
• Sustained-release microspheres for injection — LY01005, a monthly injectable microsphere suspension approved in China in 2023; not available in the U.S.
• No daily injection, solution, or oral form — unlike leuprolide, goserelin has never had a daily-injection presentation, and the peptide is not stable or absorbed by mouth
• Research-market vials — the compound circulates outside pharmacies only as an analytical reference standard or bulk API. Any such powder would be a plain aqueous presentation on reconstitution, without the polymer rod that produces the month-long release the entire clinical record depends on

This section describes formats only and is not dosing guidance.

Key considerations

• This is a licensed prescription implant, and the device is the drug. Zoladex has held FDA approval since 1989 and remains brand-only in the U.S. as of October 2026; the FDA Approved status reflects that an approved drug product containing the molecule exists. Every efficacy result above was produced by continuous release from a polymer rod placed by a clinician with a 14- or 16-gauge needle — the label carries a specific warning about injection-site and vascular injury including hemorrhage and hemorrhagic shock, with extra care advised in patients with low body mass or on full-dose anticoagulation. A reconstituted solution dosed intermittently does not reproduce that exposure; the Belchetz-era GnRH pulsatility work makes clear that intermittent agonist exposure stimulates the axis rather than suppressing it.
• The flare is a labeled hazard, not a footnote. Transient worsening of symptoms early in treatment is expected, and the label notes isolated cases of ureteral obstruction and spinal cord compression in men with prostate cancer. In the intergroup breast-cancer trial, tumor flare occurred in 16% of goserelin-treated women versus 3% after oophorectomy, and the EORTC prostate trial added a month of cyproterone acetate specifically to blunt the initial testosterone rise. Hypercalcemia in patients with bone metastases is a separate labeled warning.
• Class warnings on metabolism, heart, bone, skin, and mood. The label warns of hyperglycemia and new-onset diabetes, an increased reported risk of myocardial infarction, sudden cardiac death, and stroke in men on GnRH agonists, and QT/QTc prolongation with androgen deprivation. The label’s adverse-reaction data show bone loss in women averaging 4.3% at six months with only partial recovery a year after stopping, which is why the endometriosis course is limited to six months and the label states retreatment cannot be recommended for lack of safety data. Depression that occurs or worsens in women is a labeled warning, hypersensitivity including anaphylaxis has been reported, and the September 2025 supplement added severe cutaneous adverse reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS, AGEP) with instructions to stop permanently if confirmed. Goserelin is contraindicated in pregnancy except for palliative treatment of advanced breast cancer.
• The evidence is deep where it is deep and absent where it is absent. Goserelin’s breast-cancer benefit is established in estrogen-receptor-positive disease and was clearly inferior to chemotherapy in ER-negative disease in ZEBRA; the ovarian-protection trial enrolled only receptor-negative patients; and the metastatic comparison with surgery was underpowered by its own authors’ account. None of the goserelin trials tested the combination with an aromatase inhibitor that SOFT and TEXT examined — that combination’s evidence comes from triptorelin. Outside the gonadal axis there is no meaningful human evidence for goserelin at all.
• Naming and class confusion. Goserelin, leuprolide (leuprorelin), triptorelin, nafarelin, histrelin, and buserelin are all GnRH agonists but are different peptides with different substitutions, salts, and release systems, and “Lupron” is often used loosely for the entire class. Leuprolide is the agonist with daily-injection and multiple depot formats; triptorelin is the one that research-peptide catalogs actually stock; goserelin exists only as an implant. GnRH antagonists (degarelix, relugolix, cetrorelix) suppress the axis immediately with no flare — the opposite initial effect. ICI 118630 in older literature and LY01005 or Baituowei for the Chinese microsphere product all refer to this same molecule.