A Study of PRT3789 in Combination With Pembrolizumab in Patients With Advanced or Metastatic Solid Tumors With a SMARCA4 Mutation

The trial facts point to low odds of a clearly positive outcome. The strongest signal is currentStatus = Terminated, which materially reduces the chance of a clean, favorable readout versus an ongoing or completed study. The design also weakens positivity odds: despite being labeled Phase 2, the listed primary endpoints are Part 1 safety/tolerability measures such as DLTs and AE burden, not a defined efficacy endpoint. That makes the bar for a broadly “positive” interpretation harder to clear, especially in oncology where investors usually need credible antitumor activity in addition to manageable safety. The patient population is difficult as well: advanced or metastatic solid tumors across multiple histologies, all with SMARCA4 mutation, creates biological rationale but also substantial heterogeneity and small subgroup signal risk. Combining a novel agent with pembrolizumab may improve activity, but it also adds attribution and toxicity complexity. With primary completion already past and the study terminated, operational and disclosure risk are elevated, so I assign a low intrinsic YES probability.

This Phase 2 trial (NCT06682806) of PRT3789 + pembrolizumab is terminated. Prelude paused PRT3789 development in August 2025 after underwhelming Phase 1 monotherapy data, with the CEO citing insufficient target coverage throughout the dosing interval. By November 2025, the entire SMARCA2 degrader program was paused and the CMO departed. The company pivoted all resources to oral PRT7732, then paused that too, selling a licensing option to Incyte. The combo trial with pembrolizumab was initiated in late 2024 but terminated before meaningful enrollment or data generation could occur — no efficacy results from this combination were ever reported. The Phase 1 monotherapy showed only modest responses (5 PRs out of 32 evaluable Class 1 patients across all doses), and the decision to terminate the Phase 2 combo trial before collecting results makes positive outcome reporting essentially impossible. Terminated trials overwhelmingly do not produce positive results, especially when the sponsor has abandoned the entire program.

The trial is TERMINATED as of the current date (April 2, 2026), with the primary completion date having passed 69 days ago. This is the critical factor: when a Phase 2 trial terminates, it typically indicates the sponsor discontinued the program due to safety concerns, lack of efficacy, business decisions, or enrollment challenges. The primary endpoint is safety and tolerability measured by DLTs and AEs - if the trial were showing favorable safety data, continuation would be more likely. SMARCA4 mutations in advanced solid tumors represent an aggressive indication with high unmet need, but termination suggests the PRT3789+pembrolizumab combination did not meet sufficient benefit-risk bar. The market price at ~49.5% appears to reflect uncertainty about termination implications rather than genuine 50/50 odds. Intrinsic probability of positive results is very low given the terminated status.

The trial is terminated, which is a strong negative signal for primary endpoint success. The primary endpoints are safety and tolerability, which are typically easier to achieve than efficacy endpoints. However, termination prior to the estimated completion date suggests significant issues, likely a lack of efficacy or unacceptable toxicity in the combination. The population (SMARCA4-mutated solid tumors) is high-need but challenging. The sponsor is a small biotech (Prelude). Given termination, the probability of a positive result on the efficacy endpoints is very low, though a formal 'positive' safety readout is still a remote possibility if termination was for strategic reasons. Overall, intrinsic odds are minimal.

The trial's terminated status is a critical red flag, occurring before the estimated primary completion date (overdue by 69 days as of April 2026). Termination in Phase 2 typically signals insurmountable issues like dose-limiting toxicities, poor tolerability, enrollment failures, interim futility, or sponsor reprioritization, especially for a rare SMARCA4 mutation-enriched population (prevalent in <10% of NSCLC/esophageal cancers, limiting recruitable patients). Primary endpoints focus solely on safety/tolerability (DLT incidence in Part 1, AE severity per NCI CTCAE), with no efficacy measure as primary—efficacy is exploratory. Open-label design introduces bias, and combination with pembrolizumab heightens toxicity risk in advanced/metastatic solids. Prelude Therapeutics (small biotech PRLD) lacks resources for complex execution in multi-center setup. No results disclosed yet, but termination precludes positive readout on safety or anti-tumor activity. High disclosure risk of negative announcement, confirming operational failure and no viable path to 'positive results' (meeting primary safety or showing efficacy).

The trial's status is listed as 'Terminated' with a primary completion date approximately 69 days in the past, indicating the study ended prematurely without successfully completing its planned timeline. Terminated trials rarely yield 'positive' results in the context of market resolution, as cessation typically signals failure to demonstrate efficacy, insurmountable safety concerns, or strategic pipeline reprioritization rather than a successful outcome. The primary endpoints focus on safety and tolerability (DLTs, AEs), which are lower hurdles than efficacy, yet the study still failed to proceed to completion. SMARCA4-mutated solid tumors represent a difficult-to-treat population, and the lack of reported survival or response rate benefits combined with the termination status suggests the combination of PRT3789 with pembrolizumab did not show sufficient promise. Without evidence of a successful data readout or a shift to a later phase, the intrinsic probability of a 'positive' resolution is low.

Trial terminated 69 days after primary completion date without results disclosure. Termination at this stage typically indicates futility, safety concerns, or sponsor withdrawal due to negative data. The study was Phase 1/2 with primary endpoints focused on safety/tolerability (DLTs, AEs) rather than efficacy. No efficacy signals mentioned in summary. SMARCA4-mutant population is biomarker-limited and historically challenging. Sponsor Prelude Therapeutics (PRLD) has limited track record. Termination without pre-specified positive readout strongly suggests negative or inconclusive results. Disclosure risk is moderate—termination already public but formal results may follow. Probability of positive results: ~15%.

The phase 2 trial (NCT06682806) evaluating Prelude Therapeutics' PRT3789 in combination with pembrolizumab for advanced solid tumors with SMARCA4 mutations has a current status of "Terminated" on ClinicalTrials.gov, explicitly cited as a "Sponsor decision." A terminated clinical trial is prematurely halted before reaching its planned completion, meaning it failed to fulfill its enrollment or protocol requirements to properly evaluate the primary endpoints. In the context of clinical trial outcomes, premature termination invariably prevents the trial from declaring positive findings or achieving its primary efficacy or safety objectives successfully. The sponsor's decision to terminate typically stems from either adverse safety signals, lack of preliminary efficacy, or strategic pipeline deprioritization—none of which align with a "positive" trial outcome. Given that the trial was formally terminated without completion, the probability of the results resolving as positive is functionally zero. The market is currently heavily mispricing the probability of success at approximately 48%, seemingly ignoring the terminated status of the study. This provides a highly convicted setup for predicting an overwhelmingly negative outcome.

The trial was terminated, which generally reduces the likelihood of positive results. The study aimed to evaluate the safety and tolerability of PRT3789 in combination with pembrolizumab in patients with advanced or metastatic solid tumors with a SMARCA4 mutation. Termination often occurs due to futility, safety concerns, or operational issues, which are not indicative of a positive outcome. However, without specific details on the reasons for termination, it's challenging to assess the impact fully. The indication and intervention are innovative, but the primary endpoint focuses on safety rather than efficacy, which might suggest a cautious approach to interpreting the results.