What Are My Real Chances of Qualifying for Lu-177 PSMA Therapy If My PSMA PET Scan Shows Mixed Results — Some Lesions Positive, Some Not?

Why a Mixed Scan Feels So Confusing

You went in for a PSMA PET scan hoping for a clear answer. Instead, the report came back saying some of your cancer lesions are "PSMA positive" — they lit up on the scan — while others did not. Now you are wondering whether that means you cannot get Lu-177 PSMA therapy. That uncertainty makes sense, and you are far from alone.

The short answer is: a mixed PSMA PET scan does not automatically disqualify you. But the details matter a great deal. This article explains what "mixed results" actually means, how doctors and trial criteria interpret those results, and what questions to bring to your care team.

For a broader overview of how this therapy works, see our guide: What Is Lu-177 Therapy? A Patient-Friendly Guide to How It Works, What to Expect, and Whether It Might Be Right for You.

What "PSMA Positive" Actually Means on a Scan

PSMA stands for prostate-specific membrane antigen. It is a protein on the surface of most prostate cancer cells. Lu-177 PSMA therapy targets this protein, delivering beta radiation directly to PSMA-expressing cells. If a lesion does not express PSMA — or expresses very little — the therapy has a much weaker effect on that lesion.

A PSMA PET scan uses a radioactive tracer that binds to PSMA on cancer cells. The scanner detects where that tracer collects. Lesions that absorb a lot of the tracer appear bright — these are called "PSMA avid" or PSMA positive. Lesions that absorb little or none remain dark — these are called PSMA negative or PSMA poor.

In many men with metastatic castration-resistant prostate cancer (mCRPC), not every lesion behaves the same way. Imaging studies of mCRPC have shown that up to 30% of patients have PSMA-negative tumors, and within a single patient, different metastatic sites can show very different levels of PSMA expression. This is called PSMA heterogeneity, and it is a well-studied challenge in the field.

Why Does PSMA Heterogeneity Happen?

Prostate cancer cells are not all identical, even within one person. As the disease spreads, individual cancer clones can develop different characteristics. Some keep high PSMA expression. Others lose it.

This variation is partly driven by epigenetic changes — chemical tags on DNA that can switch gene activity on or off. Research indicates that PSMA expression heterogeneity in mCRPC likely poses a critical barrier to the success of PSMA-targeting approaches. Scientists are looking at whether certain drug combinations could restore PSMA expression in lesions that have lost it, but that work is still early.

Research also suggests that prostate cancers with defective DNA repair may produce more PSMA and could respond better to PSMA-targeting treatments. Knowing your tumor's molecular profile — including whether you carry DNA repair mutations — may be relevant to how your care team interprets your scan and plans next steps.

The key point: a PSMA-negative lesion on your scan is not a lab error or a scan failure. It is a real biological finding your oncology team needs to factor in.

The VISION Trial: The Rulebook for Current Eligibility

Most of what doctors use today to determine Lu-177 PSMA eligibility comes from the VISION trial — the phase 3 clinical trial that led to regulatory approval of this therapy. Understanding those criteria is essential to understanding your own situation.

Participants in VISION were required to have PSMA-positive mCRPC, defined as having at least one PSMA-positive metastatic lesion on PSMA PET-CT imaging. That is the positive criterion — you need at least one lesion showing meaningful PSMA uptake.

There is also a negative criterion, and this is where mixed results get complicated. The VISION trial required at least one PSMA-positive metastasis with uptake greater than liver, and excluded patients with any PSMA-negative lesion (uptake equal to or less than liver) among measurable metastases — specifically, lymph nodes larger than 2.5 cm, solid organs larger than 1.0 cm, or bone lesions with a soft-tissue component larger than 1.0 cm.

In plain language: if you had a large, visible lesion on CT that showed up PSMA negative on PET, the VISION trial would have excluded you. The concern is that a PSMA-negative lesion of meaningful size would not be targeted by the therapy and could keep growing even while other lesions respond.

To put numbers to it: in the VISION trial, 126 of 995 subjects did not meet imaging criteria. Roughly 87–90% of patients screened did meet the imaging bar, which is encouraging, but a meaningful minority did not qualify based on PET results alone.

What "Measurable" Really Means — Size Matters

Not every PSMA-negative lesion counts equally under the VISION criteria. Size thresholds matter.

A tiny bone lesion that appears PSMA negative does not automatically disqualify you. The criteria focus on measurable lesions — those large enough to be reliably assessed on CT or MRI. Small, subcentimeter findings that are negative on PSMA PET but not "measurable" by standard criteria may not be exclusionary.

This is why the exact details of your scan report — and how your nuclear medicine team or oncologist interprets it — are so important. Two patients with "mixed" scans may have very different eligibility situations depending on the size and location of their PSMA-negative lesions.

VISION Versus TheraP: Two Different Bars

Different clinical trials used different eligibility standards, so not all programs follow exactly the same rules.

In VISION, patients were eligible if they had at least one lesion with PSMA uptake greater than liver, and were excluded if they had any lesion that met CT size criteria but had lower PSMA uptake than liver. The TheraP trial required at least one lesion with a SUVmax of 20 or greater and excluded patients with discordant lesions that were FDG-positive but PSMA-negative.

TheraP used both a PSMA PET scan and an FDG (glucose-based) PET scan. FDG-PET picks up metabolically active cancer that may not express PSMA. If a lesion was FDG-positive but PSMA-negative — active cancer the therapy could not target — the patient was excluded from TheraP. This is a stricter approach to screening out patients with significant PSMA-negative disease.

Your treating team may follow VISION-like criteria, TheraP-like criteria, or a modified version used by their institution or an ongoing trial. To guide real-world use outside clinical trials, the Society of Nuclear Medicine and Molecular Imaging released a consensus statement on patient selection and appropriate use of Lu-177 PSMA. Asking your care team which criteria they use — and why — is a reasonable question.

For a closer look at what the trial evidence shows about outcomes for men with mCRPC, see: What Do the Latest Clinical Trial Results Tell Us About Lu-177 PSMA Therapy for Stage 4 Prostate Cancer — and What Do They Mean for My Treatment?

Your Other Eligibility Factors: The Scan Is Not Everything

Even if your PSMA PET results clear the imaging bar, other factors determine your overall eligibility.

The VISION trial required patients to have adequate organ function before starting therapy. VISION eligibility criteria included a white blood cell count of at least 2.5 × 10⁹/L (or absolute neutrophil count of at least 1.5 × 10⁹/L), platelets of at least 100 × 10⁹/L, and hemoglobin of at least 9 g/dL. Kidney function, liver function, and performance status were also assessed.

• Performance status: Patients generally need an ECOG performance status of 0, 1, or 2 — meaning they can carry out basic daily activities, with or without some limitation.
• Prior treatments: The original VISION approval required prior treatment with an androgen receptor pathway inhibitor (ARPI) and taxane-based chemotherapy. More recent regulatory expansions have broadened this, so your treatment history needs to be discussed with your team.
• Blood counts and organ function: Healthy enough bone marrow, kidneys, and liver are necessary because the therapy delivers some radiation dose to these organs.
• Life expectancy: Most programs require an estimated life expectancy of at least six months.

A full pre-treatment evaluation always includes blood work and imaging in addition to the PSMA scan. For background on what labs and scans are typically needed before starting therapy, you may also find our guide on DOTATATE preparation useful: What Lab Results and Scans Do I Need Before Starting Lu-177 DOTATATE — written for NETs patients, but the general principles around organ function thresholds are broadly similar.

What If You Do Not Qualify Right Now?

Not qualifying for Lu-177 PSMA therapy based on a mixed scan is not a dead end. It shapes what comes next.

First, a second opinion or specialist review at a high-volume center is reasonable. Interpretation of PSMA PET scans can vary, and a nuclear medicine specialist with specific experience in Lu-177 eligibility may read your images differently from a general radiologist.

Second, if your PSMA-negative lesions are the main obstacle, your oncologist may consider whether other treatments could shrink or control those lesions — potentially changing your eligibility later.

Third, clinical trials may use different eligibility criteria. Some trials are studying Lu-177 PSMA combined with other agents, or are designed for patients with mixed PSMA expression. Enrolling in a trial may open access that standard clinical pathways do not.

Fourth, researchers are studying whether certain drugs that restore PSMA expression could eventually help patients with heterogeneous disease qualify for therapy. This is not yet standard practice, but it signals where the science is heading.

If you are looking at broader options after hormone therapy has stopped working, our guide My Prostate Cancer Stopped Responding to Hormone Therapy — What Are My Options Before Chemotherapy? covers the treatment landscape.

How to Talk to Your Doctor About a Mixed Scan

Going into your next appointment prepared will help you get clearer answers. Consider raising these questions:

• Which of my PSMA-negative lesions are "measurable" under VISION criteria — and how big are they?
• Are any of my PSMA-negative lesions large enough to be the reason I would not qualify?
• Should I have an FDG-PET scan as well, to see whether those dark lesions are metabolically active cancer?
• Does your center follow VISION criteria, TheraP criteria, or something else?
• Are there clinical trials I might qualify for, even with mixed results?
• Is there a nuclear medicine specialist who reviews scans specifically for Lu-177 PSMA eligibility?

For a full overview of the eligibility process in plain language, see: Am I a Candidate for Lu-177 PSMA Therapy? A Plain-Language Guide to Eligibility for Men with Metastatic Castration-Resistant Prostate Cancer.

The Bottom Line

A mixed PSMA PET scan — with some positive and some negative lesions — means your case needs careful, individual review. It does not automatically close the door on Lu-177 PSMA therapy, but the details of your scan matter greatly.

The standard eligibility framework, based on the VISION trial, requires at least one lesion with meaningful PSMA uptake and excludes patients who have large, measurable lesions that are clearly PSMA negative on imaging. Where your scan falls within that framework depends on the size and number of your PSMA-negative lesions and how your team interprets them.

Push for a specialist review. Ask the right questions. And know that even if therapy is not available to you right now, the science is moving quickly and your options may change.