PSMA-1007 PET Interpretation: New Splenic Uptake Insights

Accurate interpretation of PSMA-1007 PET uptake provides essential guidance for managing biochemical recurrence in prostate cancer patients. Radiologists frequently use the PROMISE framework to standardize lesion categorization. This framework compares tracer accumulation in tumours to uptake in specific reference tissues. Consequently, identifying the normal range for these tissues remains vital for clinical precision. While parotid glands traditionally serve as the high-uptake reference, new data suggest this hierarchy may not always hold true.

Understanding Reference Tissues and PSMA-1007 PET uptake

The PROMISE criteria help clinicians grade PSMA expression using a four-point scale. Typically, clinicians compare lesions against the blood pool, liver, or spleen, and parotid glands. However, the [18F]PSMA-1007 tracer exhibits unique pharmacokinetic properties. Because the body clears this tracer primarily through the hepatobiliary system, the spleen often serves as a more reliable reference than the liver. Furthermore, experts emphasize that standardized scoring ensures reproducibility across multicenter oncology trials. Therefore, understanding patient-specific variations in reference tissue uptake remains a top priority for imaging specialists.

Clinical Challenges in PSMA-1007 PET uptake Scoring

A recent multicenter study examined 102 PET/CT scans to document normal uptake ranges. Surprisingly, 15% of patients showed higher SUVmax values in the spleen than in the parotid glands. This finding contradicts the traditional assumption that parotid uptake represents the highest reference point. Consequently, clinicians may struggle to apply the PROMISE framework as intended in these cases. Moreover, the median SUVmax for the spleen reached 15.8, whereas the parotid glands averaged 26.6. These results highlight significant interpatient variability that could influence staging. Radiologists must exercise caution when categorizing indeterminate lesions in these specific patients. Additionally, the reasons for these variations remain currently unexplained. Therefore, further research is necessary to refine reference tissue standards for this specific tracer.

Frequently Asked Questions

Q1: What is the PROMISE framework for PSMA PET interpretation?

The PROMISE framework represents a standardized system that uses reference tissues like the blood pool, liver, and parotid glands to score the intensity of tracer uptake in prostate cancer lesions.

Q2: Why is the spleen used as a reference for PSMA-1007?

Since the body clears [18F]PSMA-1007 through the liver and bile, the spleen provides a more stable and reliable semi-quantitative reference tissue compared to the liver for this specific radiotracer.

Q3: How does high splenic uptake affect clinical diagnosis?

If splenic uptake exceeds parotid gland uptake, the standard scoring hierarchy changes. This shift potentially complicates the categorization of suspicious lesions and requires careful interpretation by the reporting radiologist.

References

1. Abrahamsen BS et al. Reference tissue uptake of [18F]PSMA-1007 in positron emission tomography of recurrent prostate cancer. Eur Radiol. 2026 Apr 23. doi: 10.1007/s00330-026-12496-6. PMID: 42026330.
2. Mikó ZS et al. Different PSMA Radiopharmaceuticals: A Comparative Study of [18F]F-PSMA-1007, [18F]F-JK-PSMA-7, and [99mTc]Tc-PSMA-I&S in the Skeletal System. Pharmaceuticals (Basel). 2024 Oct 31;17(11):1458. doi: 10.3390/ph17111458.
3. Fendler WP et al. PSMA PET/CT: joint EANM procedure guideline/SNMMI procedure standard for prostate cancer imaging 2.0. Eur J Nucl Med Mol Imaging. 2023;50(5):1466-1486.

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