Novel scoring system can predict response to 177Lu-PSMA therapy in patients with mCRPC

Investigators have developed a prostate-specific membrane antigen (PSMA) PET scoring system using salivary glands as a reference organ that can effectively predict whether patients with metastatic castration-resistant prostate cancer (mCRPC) will respond to treatment with ¹⁷⁷Lu-PSMA therapy.^1,2

Complete agreement between the qPSG and vPSG scores were observed in 68% of all patients.

The tool uses a tumor-to-salivary gland ratio (PSG score) to predict outcomes. Findings on the scoring system were published in The Journal of Nuclear Medicine.

“The PSG score can enable better stratification of patients based on the response to ¹⁷⁷Lu-PSMA therapy and will assist individual clinical decision-making. These findings will be valuable in advancing precision medicine in the theranostics field,” said Jeremie Calais, MD, MSc, in a news release on the findings.² Calais is an associate professor and director of the Clinical Research Program of the Ahmanson Translational Theranostics Division at the University of California, Los Angeles.

The study recruited 237 men with mCRPC who were treated with ¹⁷⁷Lu-PSMA therapy. [68Ga]PSMA- 11 PET images were analyzed for all patients.

Investigators calculated a quantitative PSG (qPSG) score based on the ratio of whole-body to salivary gland tumor burden, and patients were categorized into groups of high (qPSG > 1.5), intermediate (qPSG = 0.5–1.5), and low (qPSG < 0.5) scores.Physician readers then interpreted the scans to assign a visual PSG score (vPSG) and again placed patients into groups of high (most legions showed higher uptake than the parotid glands), intermediate (neither low nor high), or low (most legions showed lower uptake than parotid glands) scores.

Outcomes analyzed were more than 50% of PSA decline, progression-free survival, and overall survival (OS).

Data showed that patients who had a higher PSG score were more likely to experience more than 50% PSA decline (P < .001). Both qPSG and vPSG scores were found to be independent predictors of this decline.

Patients with high scores for qPSG and vPSG were also found to have the greatest PSA progression-free survival. Median PSA progression-free survival was 7.2 months for the group with high qPSG, and 6.7 months for the group with high vPSG. The greatest OS was also observed in patients with high qPSG and high vPSG scores. Median OS was 15.0 months for the high qPSG group, and 14.3 months for the high vPSG group.

Complete agreement between the qPSG and vPSG scores were observed in 68% of all patients. Investigators concluded that scores were prognostic for PSA response and OS after treatment with ¹⁷⁷Lu-PSMA, and the vPSG and qPSG scores offered comparable prognostic value.

References

1. Hotta M, Gafita A, Murthy V, et al. PSMA PET tumor-to-salivary gland ratio to predict response to [177Lu]PSMA radioligand therapy: an international multicenter retrospective study. J Nucl Med. [published online ahead of print March 30, 2023.] Accessed April 21, 2023. doi:10.2967/jnumed.122.265242.

2. Newly developed PSG score improves patient selection for PSMA radiopharmaceutical therapy. News release. Society of Nuclear Medicine & Molecular Imaging. April 19, 2023. Accessed April 21, 2023. https://www.snmmi.org/NewsPublications/NewsDetail.aspx?ItemNumber=43729