A Better Safety Net: How PSMA PET/MRI Is Catching Hidden High-Risk Disease in Men Choosing Active Surveillance or Focal Therapy
A Pilot Study of 18F‐rhPSMA‐7.3‐PET/MRI to Reduce Mischaracterization of Active Surveillance and Focal Therapy Candidates With Occult Higher Risk Disease - Alam - The Prostate - Wiley Online Library
A landmark Northwestern University pilot trial — and a wave of supporting international research — shows that this advanced scan can find dangerous tumors standard MRI misses, changing one-in-three patients' treatment plans and dramatically boosting confidence for everyone involved.
Bottom Line Up Front (BLUF)
A new pilot clinical trial from Northwestern University found that a next-generation scan — ¹⁸F-rhPSMA-7.3 PET/MRI (brand name Posluma®) — detected hidden high-grade prostate cancer in 1 out of 4 men who appeared to be good candidates for active surveillance (AS) or focal therapy (FT) based on standard testing. The scan changed the treatment plan for 35% of patients and boosted doctor-and-patient confidence in the final decision in virtually every case. This research, published in The Prostate in February 2026, adds to a rapidly growing body of evidence suggesting PSMA PET imaging may become an important tool for men with low- or favorable intermediate-risk prostate cancer who want to avoid overtreatment without risking undertreatment.
The Problem: When "Watchful Waiting" Watches the Wrong Target
Active surveillance — the strategy of carefully monitoring low-risk prostate cancer rather than treating it immediately — has been one of the most important advances in combating overtreatment. Today, roughly 60–70% of men with low-risk disease choose AS, and data from large studies confirm that the risk of metastasis or cancer-specific death on well-managed AS programs is exceedingly low.
But AS and focal therapy rest on an assumption that can sometimes be wrong: that the cancer found on biopsy accurately represents all the cancer in the prostate. This is not always true. Multiple studies have confirmed that standard MRI — even the excellent multiparametric MRI (mpMRI) used today — misses clinically significant cancer lesions in roughly 10–30% of cases. A hidden Grade Group 3, 4, or 5 tumor lurking in a corner of the prostate that biopsy needles did not reach is precisely the kind of finding that can turn a "watchful waiting" success story into a late diagnosis.
Approximately 25–40% of men who begin AS will eventually progress to active treatment within a few years. Some of this progression is genuine cancer growth. But a meaningful portion reflects initial misclassification — the cancer was always more aggressive than it appeared at the start. The clinical term for this particularly unwelcome discovery is "extreme reclassification," meaning an upward jump to Grade Group 3 or higher. This is exactly what researchers at Northwestern University set out to detect earlier and more reliably.
What Is PSMA PET/MRI, and Why Does It Matter Here?
PSMA stands for Prostate-Specific Membrane Antigen — a protein that sits on the outer surface of most prostate cancer cells, and the more aggressive the cancer, the more PSMA it typically expresses. PSMA-targeted PET imaging works by injecting a small radioactive molecule that seeks out and "lights up" wherever PSMA-rich cells are present. Combined with MRI — which provides exquisite soft-tissue detail — the result is a two-in-one scan offering both molecular information (is cancer here?) and structural information (exactly where, and in relation to which anatomy?).
¹⁸F-flotufolastat (Posluma®, Blue Earth Diagnostics) — Also called ¹⁸F-rhPSMA-7.3. FDA-approved May 2023 based on the Phase 3 SPOTLIGHT and LIGHTHOUSE trials. Particularly notable for its low urinary excretion, reducing "noise" from the bladder near the prostate. Used in the Northwestern trial described in this article.
¹⁸F-piflufolastat (Pylarify®, Lantheus) — FDA-approved May 2021. Widely distributed nationally from centralized production facilities.
⁶⁸Ga-PSMA-11 (Illuccix®, Locametz®, Gozellix®) — The original PSMA tracer. FDA-approved 2021–2025 in various formulations. The most studied worldwide.
All three are currently FDA-approved only for detecting metastatic or recurrent disease — not yet formally approved for the active-surveillance use described in this article, which remains investigational.
The ¹⁸F-labeled tracers like Posluma hold a practical advantage for patients: fluorine-18 has a two-hour half-life, allowing centralized manufacturing and regional distribution to imaging centers that do not have an on-site cyclotron. This means broader patient access compared to the gallium-68 tracers, which require either an on-site generator or very nearby radiopharmacy.
Until recently, PSMA PET was used almost exclusively in men with advanced or recurrent prostate cancer. The idea of using it to look inside the prostate at the primary tumor — in men who otherwise appeared eligible for surveillance — is a genuinely new frontier.
The Northwestern Pilot Trial: Key Findings
Study Design
Between October 2023 and September 2024, researchers at Northwestern University Feinberg School of Medicine enrolled 20 men who met these criteria:
- NCCN low-risk or favorable intermediate-risk prostate cancer (only 3 were low-risk; 17 were favorable intermediate-risk)
- Decipher genomic score ≥ 0.45 — indicating a genomically more aggressive biology despite the favorable clinical classification
- Diagnosed after an MRI-guided biopsy with at least 10 cores sampled
- No prior prostate cancer therapy; no hip replacements or pelvic hardware
- Median age 61.9 years; median PSA 4.8 ng/mL
All 20 men received both a ¹⁸F-rhPSMA-7.3 PET/MRI scan and a standard mpMRI in the same session. Within 90 days, each man then underwent either a PET/MRI-guided biopsy (12 men) or radical prostatectomy (8 men) to confirm what the scan found.
The critical question: Would the PSMA PET/MRI detect Grade Group 3–5 disease, seminal vesicle invasion, or lymph node involvement that standard testing had missed? The researchers decided that finding this outcome in even 3 out of 20 patients (15%) would be clinically significant — meaning it would justify serious attention from the field.
Results: 1 in 4 Men Had Hidden High-Grade Disease
Five of 20 patients — 25% — had higher-grade disease found that had not been identified by prior testing. The specific upgrades were: one patient went from Grade Group 1 to GG 3; one jumped from GG 1 all the way to GG 5; two went from GG 2 to GG 3; and one went from GG 2 to GG 4. Every one of these five men had a PET-avid lesion visible on the scan. None of the eight surgical patients had spread to the seminal vesicles or lymph nodes — a reassuring finding for this population.
The "Invisible Lesion" Problem
Perhaps the most striking finding involved five men (25%) who had PET-positive lesions that their pre-enrollment MRI had simply not seen. In two of these cases, the mpMRI was entirely negative (PI-RADS 1 or 2 — essentially normal). In three others, the PET found lesions in completely different parts of the prostate than where the MRI had pointed. Three of these five men were ultimately upgraded. This is exactly the scenario AS and FT patients most fear: a dangerous tumor hiding where conventional imaging does not look.
Treatment Decisions Changed — and Confidence Soared
Before the scan, six of the 20 patients (30%) were essentially undecided about their treatment path, with low confidence. After the scan, major treatment plan changes occurred in seven patients (35%). Six of the previously undecided patients moved toward definitive treatment — three chose surgery and three chose focal therapy. One patient moved from planned active surveillance to radiation therapy.
The confidence data were striking. Before scanning, the group averaged a "moderate" confidence score of 2.05 out of 3. After scanning, confidence rose to 2.80 — statistically significant (p < 0.001) — and no patient ended the process with low confidence in their plan. All five men who chose focal therapy did so with high confidence. As the authors note, this psychological dimension — the reduction of anxiety around treatment decisions — may matter nearly as much as the oncological findings themselves.
Safety: Minimal Side Effects
Four of 20 patients (20%) experienced mild (Grade 1) side effects possibly related to the injection: three reported nausea and one had both nausea and a headache. All resolved on their own within 24 hours, with no lasting effects. This is consistent with the safety profile established in the large Phase 3 SPOTLIGHT and LIGHTHOUSE trials.
- 25% of patients had occult Grade Group 3–5 disease detected (exceeded the 15% threshold for clinical significance)
- 25% had PET-positive lesions entirely missed by prior mpMRI
- 35% experienced a major change in their treatment plan
- Physician-patient confidence improved from moderate to high (p < 0.001)
- No serious adverse events; only mild, self-resolving side effects in 20%
- Median Decipher score 0.58 — all patients selected for elevated genomic risk
What the Rest of the World Is Finding: Converging Evidence
The Australian CONFIRM Trial
The Northwestern study does not stand alone. The prospective CONFIRM trial, conducted across multiple Australian centers and reporting early results in 2025, used PSMA PET/CT in men on active surveillance with "high-risk features" — such as elevated PSA density or a PI-RADS 4–5 lesion — who were undergoing a confirmatory biopsy. The early CONFIRM findings aligned closely with the Northwestern results: PSMA PET/CT improved risk stratification by identifying both disease progression and MRI-occult lesions, and confirmed the absence of high-risk disease in men who were truly suitable to stay on surveillance. The trial's principal investigators concluded that the scan improved the "safety" of active surveillance for carefully selected patients.
The Systematic Review Picture
A comprehensive 2025 review published in the Journal of Clinical Medicine synthesized the available literature on PSMA PET in active surveillance. Reviewing multiple studies, the authors found that PSMA PET identified MRI-occult lesions in 12–29% of low-to-intermediate risk patients, of which up to 10% harbored genuinely unfavorable pathology that would likely make them unsuitable for ongoing AS. A separate systematic review found that adding PSMA PET to standard MRI boosted the sensitivity for detecting clinically significant cancer from 83% to 97%, and improved the negative predictive value from 72% to 91%. For men and their doctors trying to feel confident that AS is truly safe, those improvements in the negative predictive value — the scan's ability to give genuine reassurance when negative — are particularly meaningful.
The Lancet Oncology: A New Risk Classification System
In a major development published in early 2026, an international registry-based study in The Lancet Oncology proposed entirely new prostate cancer risk groups based on PSMA-PET findings, using data from thousands of patients spanning over a decade. Dubbed the "PPP3" nomograms, this work argues that conventional risk classification (built around PSA, Gleason grade, and clinical staging) is becoming outdated as PSMA PET enters routine practice — because PET can detect disease that conventional imaging completely misses, and this undetected disease significantly affects prognosis. The implication for AS patients: the field is moving toward a future where PSMA PET findings will need to be incorporated into risk groupings used to counsel patients about surveillance eligibility.
PSMA PET After Focal Therapy: Surveillance Gets Smarter
PSMA PET's value does not end at the treatment decision. A 2025 narrative review in the World Journal of Urology evaluated how PSMA PET/CT and PET/MRI can be used for surveillance after focal HIFU treatment — one of the leading focal therapy technologies. The review found that PSMA PET metabolic imaging outperforms PSA testing alone and provides complementary information to mpMRI in detecting residual or recurrent disease after focal ablation. For patients who choose focal therapy, knowing that this same imaging platform can also monitor them afterward is reassuring.
A Note of Caution: Evidence Is Still Building
Not all experts are enthusiastic about rapidly expanding PSMA PET use. A September 2025 analysis in Medscape quoted prominent oncologists who note that no Phase 3 trial has yet demonstrated that treating disease found only by PSMA PET actually improves survival or quality of life, compared to not treating it. "You can expose patients to treatments they may not need at that time," one expert cautioned. A 2025 commentary in the Société Internationale d'Urologie Journal reviewing data on PSMA PET in favorable intermediate-risk cancer specifically found "low yield and cost" in routine use for this group, and advised against making it a standard tool without further evidence. The Northwestern trial itself was designed with a very specific, genomically enriched population (Decipher ≥ 0.45); the authors caution that "expanded studies will be necessary to determine if PET imaging has clinical utility in all men considering AS or FT, regardless of disease biology." Insurance coverage for this indication remains inconsistent, and out-of-pocket costs can be substantial.
The Decipher Connection: Who Might Benefit Most?
One of the most clinically useful aspects of the Northwestern trial is its focus on a specific high-yield population: men with a Decipher genomic score ≥ 0.45. The Decipher test analyzes the genetic activity of the biopsy tissue to predict how biologically aggressive the cancer is likely to behave, independent of Gleason grade alone. Men with a Decipher score in the intermediate (0.45–0.60) or high (>0.60) range who nonetheless appear clinically favorable are precisely the patients where a mismatch may exist between appearance and reality — and where additional imaging might reveal hidden risk.
The researchers were explicit that this Decipher threshold was chosen to enrich the study with patients most likely to benefit from additional testing. Whether PSMA PET should be used more broadly — in all men considering AS, regardless of genomic risk — remains an open research question, and one the field is actively working to answer.
Why Posluma (¹⁸F-rhPSMA-7.3)? What Makes This Tracer Special for Prostate Imaging?
Among the approved PSMA PET tracers, the Northwestern team chose ¹⁸F-rhPSMA-7.3 (brand name Posluma, made by Blue Earth Diagnostics, a Bracco company) for a specific technical reason: it has significantly lower urinary excretion than most competing agents. The bladder sits directly above and behind the prostate. When a PET tracer accumulates heavily in urine, its radioactivity can spill over and obscure structures in and around the prostate — exactly the area of greatest interest in this patient population. Posluma's low bladder activity reduces this "volume averaging artifact," making small intraprostatic lesions much easier to see clearly.
The tracer has also demonstrated very high inter-reader reproducibility for intraprostatic lesions in the primary staging setting — meaning that when two different physicians read the same scan, they tend to agree on what they see. This reproducibility is critical for a tool intended to guide major treatment decisions. Posluma received FDA approval in May 2023, based on the Phase 3 SPOTLIGHT trial (biochemical recurrence) and LIGHTHOUSE trial (newly diagnosed higher-risk cancer). It is now incorporated into NCCN guidelines as one of three recommended PSMA tracers.
The Bigger PSMA Picture: FDA Approvals, Guidelines, and What's Coming
The arrival of PSMA PET imaging has been one of the most significant developments in prostate cancer management in a generation. In the landmark randomized proPSMA trial from Australia, PSMA PET/CT showed 85% sensitivity and 98% specificity for prostate cancer metastases — compared to only 38% sensitivity for conventional bone-plus-CT scanning. This superiority has driven rapid uptake.
The current NCCN guidelines (v1.2025 and v2.2026) now include PSMA PET as the preferred or co-preferred imaging option for initial staging of unfavorable intermediate-, high-, and very-high-risk disease, for detection of biochemical recurrence after surgery or radiation, and for evaluation of patients being considered for Lu-177 PSMA radioligand therapy (Pluvicto). The NCCN panel explicitly states that for many of these indications, PSMA PET can be used directly as a front-line tool without conventional imaging as a prerequisite. The American Urological Association and Society of Urologic Oncology guidelines similarly recommend PSMA PET preferentially for patients with PSA recurrence after primary therapy.
The use of PSMA PET in the early, localized, surveillance-eligible setting described in this article remains off-label and investigational under current FDA approvals. The Northwestern trial and the CONFIRM trial represent the vanguard of the evidence needed to potentially expand approved indications in the future.
Questions to Discuss With Your Doctor
- Has my Decipher genomic score been obtained? Would a score ≥ 0.45 change how we think about additional imaging?
- Am I at a center that offers PSMA PET/MRI — the combined modality? Or only PET/CT?
- Would a PSMA PET scan before my confirmatory biopsy or treatment decision be appropriate in my specific case?
- If a PET scan finds a lesion my MRI missed, how would that change my treatment options?
- What is the out-of-pocket cost if my insurance does not cover this use? (Current coverage for AS/FT indications is not standard.)
- Is there a clinical trial I could enroll in that would provide this imaging as part of a research protocol?
Conclusion: A Promising but Still-Developing Tool
The Northwestern University pilot trial adds meaningful, prospectively collected evidence to a rapidly evolving field. For men with favorable-risk prostate cancer who are considering active surveillance or focal therapy — especially those whose genomics suggest hidden biological aggression — PSMA PET/MRI appears capable of finding disease that standard MRI and biopsy alone would miss, and of giving both patients and their physicians greater confidence in whatever treatment path they choose.
This is not yet a standard-of-care recommendation. The study enrolled only 20 patients, all selected for elevated genomic risk. Coverage is inconsistent. And the ultimate test — whether acting on PSMA PET findings in this early-stage population actually improves long-term outcomes — still awaits larger, longer trials. But the signal is compelling, the technology is FDA-approved for other prostate cancer indications and is becoming more widely available, and the researchers' call for "expanded investigations into PSMA-PET-based imaging in favorable risk men with localized prostate cancer" is well-founded.
For members of the IPCSG community navigating the complex decision between watchful waiting and active treatment, this research represents exactly the kind of tool — used thoughtfully, with full awareness of its current limits — that can help turn an anxiety-filled gray zone into a clearer, more confident path forward.
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