The J&J JNJ-6143 prostate cancer study reported that an experimental once-daily pill produced a 50% or greater fall in prostate-specific antigen (PSA) in 77% of patients at the 50 mg dose, including people whose disease had already progressed through several earlier treatments. Johnson & Johnson presented the Phase 1 data at the ESMO 2026 congress, and the drug remains investigational. Early-stage results involve small numbers and short follow-up, so they show activity and not proven benefit.
Key takeaways from the J&J JNJ-6143 prostate cancer trial
- 77% of patients at the 50 mg dose had a confirmed PSA fall of at least 50% (PSA50); 48% had a fall of at least 90%.
- Among patients with measurable tumours, confirmed complete or partial response was reported as 69% in some reports and 75% (12 of 16) in the company release.
- JNJ-6143 is an oral RIPTAC, a new type of molecule that links the androgen receptor to a survival protein called BRD4.
- Patients had metastatic prostate cancer that had progressed after androgen receptor pathway inhibitors, with a median of four earlier therapies.
- The 50 mg dose is moving into further development, and a Phase 2 study is planned or under way.
Why the numbers differ in the J&J JNJ-6143 prostate cancer reports
The brief for this story described 31 evaluable patients at 50 mg, a 77% PSA response and a 69% confirmed tumour response. The company’s own release describes 38 patients treated at 50 mg, a 77% PSA response and a 75% tumour response, which is 12 of 16 patients with measurable disease. The two sets of figures are probably based on different data cutoffs or definitions of evaluable patients, but the sources we read do not say so.
Our own arithmetic offers a clue. Seventy-seven percent of 31 patients is about 24 patients, which is a whole number, while 77% of 38 is not. Likewise, 11 of 16 is 69% and 12 of 16 is 75%. That pattern suggests the 31-patient and 69% figures come from an earlier cut of the data and the 38-patient and 75% figures from a later one. This is our inference and not a statement from the company, so we report both and attribute each.
How the J&J JNJ-6143 prostate cancer study was designed
The study is a multicentre Phase 1 dose-escalation and dose-expansion trial (NCT06800313). Doses in the escalation part ran from 12.5 mg to 150 mg once daily. In the expansion part, patients were randomised one to one to 25 mg or 50 mg once daily, and 50 mg was identified as the preliminary optimal dose. Endpoints included safety, pharmacokinetics, anti-tumour activity and the optimal dose. The registry entry is on ClinicalTrials.gov.
Participants had metastatic prostate cancer resistant to androgen pathway modulation, also called metastatic castration-resistant prostate cancer, and had progressed after one or more androgen receptor pathway inhibitors. They had received a median of four earlier therapies, including chemotherapy and PSMA-targeted radioligand therapy, according to the company.
Efficacy: what PSA response and tumour response mean
- PSA50: 77% at 50 mg; PSA90: 48%. PSA is a blood marker that usually falls when prostate cancer responds to treatment.
- Tumour response in patients with measurable disease: 69% (trade-press report) or 75% (12 of 16, company release), by standard imaging criteria.
- PSA reductions were also seen in patients with high-risk molecular features, according to the company.
PSA and imaging responses are early signals. Neither is the same as longer survival, and the group with measurable disease was only 16 patients, so one patient changes the percentage by about six points.
Safety of JNJ-6143 in the Phase 1 study
At 50 mg, the most common treatment-related side effects were raised cholesterol (18%), nausea (16%) and raised triglycerides (16%), and most were mild to moderate, the company reports. Four patients (11%) had dose interruptions, one (3%) had a dose reduction and one (3%) stopped treatment because of side effects. About 71% remained on treatment at the data cutoff, and median follow-up was 5.6 months. Longer follow-up and larger studies are needed to assess safety.
What makes the J&J JNJ-6143 prostate cancer drug different
Most hormone-targeted prostate cancer drugs block or reduce androgen receptor signalling. A RIPTAC (Regulated Induced Proximity Targeting Chimera) works differently: it forms a complex between the androgen receptor, which is abundant on prostate cancer cells, and BRD4, a protein cells need to survive. The aim is to disrupt cell function and trigger cell death in cells that carry the receptor. JNJ-6143 is the first RIPTAC to enter clinical studies, according to the company. J&J acquired Halda Therapeutics, which developed the compound, in December 2025.
Timeline of the J&J JNJ-6143 prostate cancer programme
- December 2025: Johnson & Johnson completes its acquisition of Halda Therapeutics.
- 24 October 2026: results presented at ESMO 2026 (abstract 2216O).
- 25 October 2026: company press release with updated figures.
- Next: further development at 50 mg and a Phase 2 study (NCT07832292).
Quotes from the investigators and J&J
Johann de Bono of the Institute of Cancer Research in London said the team is seeing meaningful anti-tumour activity in patients who have already received multiple therapies. Yusri Elsayed, global head of oncology therapeutics at J&J, said the compound brings a fundamentally different oral mechanism to the company’s prostate cancer pipeline. Both statements come from the company release. More on the company is at jnj.com.
General background: advanced prostate cancer
Prostate cancer that has spread and stopped responding to hormone therapy is hard to treat, and options narrow after several lines. The US National Cancer Institute explains the disease and its treatments on its prostate cancer page. New mechanisms are sought for patients whose tumours have become resistant to androgen receptor inhibitors. See also our Pharmaceutical coverage.
Our analysis of the J&J JNJ-6143 prostate cancer data
In our assessment, the J&J JNJ-6143 prostate cancer results are encouraging for a Phase 1 trial because the response rates are high in a heavily pretreated group and the drug is an oral pill with a novel mechanism. The limitations are equally clear: a small sample, short follow-up, a company-reported analysis, and inconsistent figures across reports. Response rates in early trials often fall in larger studies, so we do not predict later results.
What is not disclosed about the J&J JNJ-6143 prostate cancer trial
- Duration of response and progression-free survival.
- The PSA50 rate and patient numbers behind each cut of the data.
- Phase 3 plans or timelines.
- Pricing or regulatory strategy.
Risks and caveats of the J&J JNJ-6143 prostate cancer data
JNJ-6143 is investigational and not approved. Results are from a company release and a congress presentation as reported, not from a peer-reviewed paper. Figures differ between reports. This article is news reporting and not medical advice; patients should speak to their oncologist about options and clinical trials.
What to watch next after the J&J JNJ-6143 prostate cancer trial
- Phase 2 results at the 50 mg dose.
- Longer follow-up and durability of response.
- A peer-reviewed publication of the Phase 1 data.
- Competing oral and radioligand approaches in prostate cancer.
FAQ
What did the J&J JNJ-6143 prostate cancer trial show?
A PSA fall of at least 50% in 77% of patients at 50 mg, and confirmed tumour responses in roughly 69% to 75% of those with measurable disease.
Is JNJ-6143 approved?
No. It is an experimental drug in early clinical trials.
What is a RIPTAC?
A molecule that brings the androgen receptor and a survival protein together to trigger death of cancer cells that carry the receptor.
How we reported this: we relied on the Johnson & Johnson release, the congress presentation as reported, the trial registry and NCI background, and attributed every claim. Last updated 27 October 2026. This is news reporting and not advice.