Sometimes the market does something that makes you wonder if everyone read the same press release. Janux Therapeutics Inc. (JANX) watched its stock crater to a 52-week low on Tuesday after releasing clinical trial data that, on paper at least, looked pretty encouraging. The shares fell nearly 48% despite the company reporting positive updates on its prostate cancer treatment.
Here's what actually happened: Janux shared updated interim results from its Phase 1 trial testing JANX007 in patients with metastatic castration-resistant prostate cancer (mCRPC). As of the October 15, 2025 data cutoff, 109 patients had been treated across the Phase 1a dose escalation portion and the Phase 1b expansion trials.
The patient populations tell an important part of the story. Those in the Phase 1a trial were heavily pre-treated, having gone through a median of four prior therapies before trying JANX007. The Phase 1b expansion enrolled taxane-naïve mCRPC patients, meaning they hadn't yet received that class of chemotherapy.
What the Data Actually Showed
Patients across the Phase 1 trials demonstrated high prostate-specific antigen (PSA) response rates with deep PSA declines. For context, PSA levels are a key marker doctors watch in prostate cancer treatment. Among patients whose tumors could be evaluated using RECIST criteria (the standard way of measuring tumor response), 30% showed confirmed or unconfirmed partial responses—that's 8 out of 27 evaluable patients.
The durability data looked solid too. Radiographic progression-free survival (rPFS) ranged from 7.9 to 8.9 months across different dosing schedules. Patients receiving treatment every two weeks (Q2W) showed favorable rPFS compared to those on weekly dosing.
The preliminary Phase 1b data in taxane-naïve patients showed rapid and deep PSA reductions, primarily with grade 1 cytokine release syndrome (CRS)—the mildest category of this side effect. Analysis of tumor burden suggested the potential for improved rPFS in patients treated earlier in their disease course.
On the safety front, JANX007 demonstrated a manageable profile. CRS, the main side effect to watch with this type of therapy, was primarily limited to the first treatment cycle and stayed at grades 1 and 2 (mild to moderate). The company identified a CRS mitigation strategy that maintains this favorable safety profile.
Where Janux Goes From Here
The company plans to advance JANX007 with a focus on monotherapy and combinations with darolutamide in taxane-naïve mCRPC patients. Janux also intends to evaluate the treatment in PARP inhibitor-refractory patients, which could potentially open a path to expedited regulatory approval.
Why Analysts Think the Market Got It Wrong
William Blair analyst Matt Phipps called the stock plunge an overreaction, arguing that the totality of data across multiple dosing regimens and CRS mitigation strategies paints a more positive picture than the market reaction suggests.
"While there are some fair criticisms, such as the decline in RECIST response rate and not disclosing confirmed versus unconfirmed responses, focusing on the cohorts of patients treated with dosing regimens advancing to Phase Ib and initial data in patients with lower tumor burden continue to suggest JANX007 has the potential to achieve a best-in-disease profile and achieve blockbuster sales," Phipps noted.
William Blair expects the next JANX007 update from the Phase Ib trial to come in 2026, which should help reestablish investor confidence in the program. Phipps views the selloff as a buying opportunity and maintains an Outperform rating on the stock.
Janux Therapeutics shares closed at $17.73 on Tuesday, down 47.82% for the day.
