Using [68Ga]Ga-PSMA-11 PET/CT to monitor treatment response in prostate cancer patients can offer important lesion-based insights over prostate-specific membrane antigen (PSMA)-based monitoring, according to a new study published in EJNMMI Research.
“[68Ga]Ga-PSMA-11 PET/CT is an effective imaging modality for the staging of intermediate- and high-risk (prostate cancer) PCa and for the assessment of patients with biochemical failure,” wrote Jonathan Kuten, of Tel-Aviv Sourasky Medical Center’s Department of Nuclear Medicine and colleagues. “The role of [68Ga]Ga-PSMA-11 PET/CT in monitoring response to treatment in PCa remains unclear due to the lack of relevant data, with few reports having addressed this issue.”
Additionally, Kuten et al. noted, traditional assessment methods such as the Response Evaluation Criteria in Solid Tumors (RECIST) have limitations when evaluating small lesions.
For their study, the researchers retrospectively investigated 52 patients with metastatic prostate cancer who underwent [68Ga]Ga-PSMA-11 PET/CT imaging and serum prostate-specific antigen (PSA) level measurements prior to, and following treatment. Patient response was categorized by serum PSA changes according to improvement, stable disease and disease progression, which was then compared to change in imaging findings on pre- and post-treatment scans.
A majority (65.4%) of patients had compatible biochemical- and imaging-based response to treatment. PET/CT, however, revealed progressive disease in 9.6% of patients and improvement/ stable disease in a quarter of patients compared to biochemical assessments.
This discrepancy was most notable in biochemically stable patients (90.9%) followed by those with biochemical progression (33.3%).
Kuten and colleagues pointed out that imaging-based assessment allowed for additional, and important insight into individual lesions.
“A major added value of imaging in monitoring response is that it allows lesion-based and not only patient-based analysis,” the researchers wrote. “Progression of some lesions may be obscured by a favorable response of other lesions, resulting in stable PSA levels in patients with heterogeneous lesion responses.
Imaging of lesions may better assist in risk stratification and identification of lesions requiring special attention, as well as for tailoring of the radiation field.”
There were a few limitations to the study, including its prospective design, the researchers acknowledged. The group also noted that PSMA imaging costs are much higher than those associated with PSA measurement, and therefore, should not be used in all situations.
“As the costs associated with PSMA imaging are substantially higher than PSA measurement, the former should be judiciously used when clinically-relevant, e.g., when post-treatment clinical assessment and biochemical response are discrepant, as well as whenever targeted therapy to some diseased areas is considered,” the authors concluded.