From the Guidelines
Androgen deprivation therapy (ADT) can significantly alter PSMA PET scan results in prostate cancer metastatic workup, with studies showing increased detection rates with ADT 1.
Key Findings
- The detection rate of PSMA PET scan increases with ADT, as reported by Einspieler et al, with a detection rate of 97.7% in ADT-positive patients compared to 86.3% in ADT-negative patients 1.
- ADT typically decreases PSMA expression in prostate cancer cells, which can lead to reduced visibility of metastatic lesions on PSMA PET imaging.
- For optimal PSMA PET scan results, it is recommended to perform imaging before starting ADT when possible, as suggested by the study 1.
Clinical Implications
- If a patient is already on ADT, clinicians should be aware that the scan may underestimate the extent of disease.
- In cases where ADT has been initiated but accurate staging is crucial, some specialists suggest a minimum 3-month washout period before PSMA PET imaging, though this must be balanced against the risks of treatment interruption 1.
- The mechanism behind this effect involves the androgen receptor pathway, which regulates PSMA expression - when testosterone is suppressed by ADT, PSMA expression decreases, resulting in lower radiotracer uptake on PET scans.
Recommendations
- Perform PSMA PET scan before starting ADT when possible.
- Be aware of the potential underestimation of disease extent in patients already on ADT.
- Consider a minimum 3-month washout period before PSMA PET imaging in cases where accurate staging is crucial, weighing the risks and benefits of treatment interruption 1.
From the Research
Effect of ADT on PSMA PET Scan
- The effect of androgen deprivation therapy (ADT) on PSMA PET scan in prostate cancer metastatic workup has been studied in several research papers 2, 3, 4, 5, 6.
- A prospective study found that short-term ADT increases PSMA uptake in bone metastases, with a mean increase of 77% in SUVmax 2.
- Another study found that long-term ADT reduces the visibility of castration-sensitive prostate cancer on PSMA PET/CT, with a decrease in tracer uptake values in 71% of lesions 3.
- A feasibility study found that low-dose ADT may enhance PSMA uptake in patients with biochemical recurrence and low PSA levels, with an increase in SUV in PSMA-positive lesions in two patients 4.
- A retrospective analysis found that neoadjuvant ADT causes a significant decrease in serum PSA values and SUVmax of primary tumor and metastatic lymph nodes in non-metastatic prostate cancer patients 5.
- A phase 2 trial found that PSMA PET/CT and planar bone scan plus CT have identical bone metastasis detection rates in patients with biochemical progression during ADT, with 100% agreement between the two scans 6.
Implications for PSMA PET Scan Interpretation
- The studies suggest that ADT can alter PSMA PET scan results, with both increases and decreases in tracer uptake values observed 2, 3, 4, 5.
- The optimal imaging time point after ADT initiation may be 3 to 4 weeks, as suggested by one study 2.
- The use of ADT may not interfere with the interpretation of PSMA PET scan results, as none of the metastases with decreasing SUVmax disappeared in one study 2.
- The studies highlight the importance of considering the effects of ADT on PSMA PET scan results when interpreting scans in patients with prostate cancer 2, 3, 4, 5, 6.