Can ^18F‑PSMA PET imaging be used for cancers other than prostate cancer?

Can F18-PSMA PET Be Used for Cancers Apart from Prostate Cancer?

F18-PSMA PET imaging can detect certain non-prostatic malignancies, but its clinical utility remains limited and should not be routinely used outside prostate cancer except in highly selected research settings. While PSMA expression occurs in the tumor neovasculature of various solid tumors, the evidence for clinical benefit in non-prostatic cancers is insufficient to support routine use 1.

Current Evidence for Non-Prostatic Cancers

Tumors with Documented PSMA Uptake

The most promising data exist for:

• Clear cell renal cell carcinoma: Shows improved diagnostic accuracy compared to standard imaging, with documented changes in patient management 1
• Adenoid cystic carcinoma of salivary glands: Demonstrates comparable improvements in staging accuracy 1
• Hepatocellular carcinoma and glioblastoma: PSMA-PET shows diagnostic accuracy comparable to contrast-enhanced CT/MRI, potentially useful when morphological imaging is equivocal 1
• Iodine-refractory thyroid carcinoma: High PSMA uptake identified, suggesting potential for PSMA-targeted therapy 1
• Triple-negative breast carcinoma: Shows PSMA avidity, warranting investigation for therapeutic applications 1

Documented Incidental Findings

Case reports demonstrate PSMA uptake in:

• Brain metastases from lung adenocarcinoma 2
• Papillary thyroid carcinoma (incidentally detected during prostate cancer staging) 3
• Esophageal squamous cell carcinoma 4
• Follicular lymphoma 5
• Pancreatic ductal adenocarcinoma 6

Critical Limitations

Pancreatic Cancer: A Cautionary Example

The PANSCAN-2 trial 6 specifically evaluated F18-PSMA PET/CT in potentially resectable pancreatic cancer and found:

• Low tracer uptake (mean SUVmax 5.0 ± 1.3)
• Zero detection of lymph node metastases despite 8 patients having histologically confirmed nodal disease
• Zero detection of distant metastases despite 2 patients having confirmed metastatic disease
• No correlation between PET uptake and tissue PSMA expression
• Conclusion: Added value appears limited

General Limitations Across Tumor Types

• PSMA uptake is not specific to malignancy—benign conditions also show uptake 7
• Uptake intensity varies significantly by tumor type and histology 1
• Lower LAT-1 expression in adenocarcinomas may reduce sensitivity 8
• Mucinous tumors typically show low uptake 8
• No established interpretation frameworks exist for non-prostatic cancers
• Lack of prospective data on impact on patient outcomes 1

Clinical Recommendation Algorithm

For routine clinical practice:

1. Do not order F18-PSMA PET for non-prostatic cancers outside clinical trials
2. Use established imaging modalities per tumor-specific guidelines (e.g., FDG-PET for most solid tumors)

If incidental non-prostatic uptake is found on prostate cancer staging:

1. Document the finding with SUVmax and anatomic location
2. Correlate with standard imaging (CT/MRI)
3. Pursue tissue diagnosis if clinically indicated based on standard criteria
4. Do not assume malignancy based solely on PSMA uptake

Potential exceptions requiring multidisciplinary discussion:

• Clear cell renal cell carcinoma when considering PSMA-targeted therapy in clinical trials
• Adenoid cystic carcinoma of salivary glands in research settings
• Iodine-refractory thyroid cancer being considered for experimental PSMA-directed therapy

Common Pitfalls to Avoid

1. Assuming PSMA specificity: PSMA uptake does not equal prostate cancer metastasis—always consider alternative diagnoses 5, 3
2. Overestimating sensitivity: The pancreatic cancer data 6 demonstrates that negative PSMA-PET does not exclude metastatic disease
3. Ignoring established guidelines: Current prostate cancer guidelines 9, 10 only endorse PSMA-PET for prostate cancer staging and biochemical recurrence
4. Premature clinical application: Despite promising research 1, larger prospective studies assessing longitudinal patient outcomes are needed before routine clinical use

The evidence consistently shows that while PSMA-PET can detect various non-prostatic malignancies, it should remain a prostate cancer-specific tool in routine practice until definitive prospective data demonstrate clinical benefit in other tumor types.