Study compares single photon emission CT with 18F-PSMA-PET/CT in prostate cancer

Although single photon emission computer tomography (SPECT/CT) with ^99mTc‐PSMA-SPECT/CT had a slightly lower rate of lesion detection versus ¹⁸F-PSMA-PET/CT, this difference had no impact on clinical staging, suggesting the cost-effective modality may be a viable alternative for the primary diagnosis of prostate cancer in areas with limited income and access.

“^99mTc‐PSMA-SPECT/CT is useful in primary diagnosis of prostate cancer. Despite its slightly lower lesion detectability compared to ¹⁸F-PSMA, it did not impact the clinical staging and consequently, the initial treatment intention,” the authors wrote in their poster conclusion.

The findings came from a small, prospective study presented in a poster session at the 2024 ASCO Genitourinary Cancers Symposium.¹

Describing the background of their study, the authors explained that ⁶⁸Gallium- and ¹⁸Fluorine-based PSMA-PET imaging has demonstrated superiority over conventional imaging and is revolutionizing the paradigm for the diagnosis and staging of prostate cancer. However, the high demand and cost of these agents can make it challenging to access them. Given these circumstances, the authors explained that interest has increased in 99mTechnetium-labeled-PSMA agents, as “SPECT/CT is more available worldwide and the imaging agent is low cost.”¹ Accordingly, the researchers launched this study to compare ^99mTc‐PSMA-SPECT/CT and ¹⁸Fluorine-based PSMA-PET to determine the potential of using the former as an alternative in this setting.

The study included 16 patients with intermediate unfavorable and high-risk prostate cancer that was histologically confirmed. The mean patients age was 71 years (range, 54-75) and the median PSA level at baseline was 31.5 ng/mL (range, 4.3-920).

All patients received ¹⁸F-PSMA-PET/CT and ^99mTc‐PSMA-SPECT/CT. For the purpose of the study, lesions were divided into prostate, seminal vesicles, locoregional lymph nodes, non-locoregional lymph nodes, bone metastases, and visceral metastases. “Volumetric analysis was also performed between the two imaging modalities (Tumoral Total Volume [TTV]) and correlated with PSA levels,” the researchers wrote on their poster.¹

¹⁸F-PSMA-PET/CT detected 233 lesions, including prostate (n = 16), seminal vesicles (n = 11), locoregional lymph nodes (n = 54), non-locoregional lymph nodes (n = 66), bone (n = 82) and visceral (n = 4). ^99mTc‐PSMA-SPECT/CT detected 100% of the prostate (16/16), seminal vesicles (11/11), and visceral (4/4) lesions. The detection rate was less than 100% for ^99mTc‐PSMA-SPECT/CT for locoregional lymph nodes (51/54; 94%), non-locoregional lymph nodes (51/66; 77%), and bone lesions (70/82; 85%).

Volumetrics analysis showed that any differences between TTV SPECT and TTV PET were not statistically significant (t = –0.021; P = .49). Further, “All patients were classified according to miTNM showing no difference,” the authors wrote.¹

The researchers noted that the smallest diameter of a positive lymph-node lesion detected by SPECT/CT was 4 mm (range, 4-18). Additionally there were 5 patients with high-volume disease that was detected by both ¹⁸F-PSMA-PET/CT and ^99mTc‐PSMA-SPECT/CT.

“^99mTc‐PSMA-SPECT/CT is useful in primary diagnosis of prostate cancer. Despite its slightly lower lesion detectability compared to ¹⁸F-PSMA, it did not impact the clinical staging and consequently, the initial treatment intention,” the authors wrote in their poster conclusion.¹

There are currently 2 ¹⁸F-based PSMA products approved by the FDA. Piflufolastat F 18 (Pylarify)² and flotufolastat F 18 (Posluma)³ are both approved for use in patients with suspected prostate cancer metastasis who are potentially curable by definitive surgery or radiation, and patients with suspected prostate cancer recurrence based on elevated PSA levels.

References

1. Vargas Ahumada JE, Scavuzzo A, González Rueda SD, et al. Prostate-specific membrane antigen SPECT-CT in patients with intermediate and high-risk prostate cancer in primary diagnosis: A comparative analysis with 18F-PSMA PET/CT. J Clin Oncol 42, 2024 (suppl 4; abstr 43). doi: 10.1200/JCO.2024.42.4_suppl.43

2. Lantheus receives U.S. FDA approval of PYLARIFY® (piflufolastat F 18) injection, the first and only commercially available PSMA PET imaging agent for prostate cancer. Published online May 27, 2021. Accessed October 5, 2023. https://investor.lantheus.com/news-releases/news-release-details/lantheus-receives-us-fda-approval-pylarifyr-piflufolastat-f-18

3. US FDA approves Blue Earth Diagnostics’ Posluma (flotufolastat F-18 injection, first radiohybrid PSMA-targeted PET imaging agent for prostate cancer. News release. Blue Earth Diagnostics. May 30, 2023. Accessed October 5, 2023. https://www.businesswire.com/news/home/20230530005180/en/U.S.-FDA-Approves-Blue-Earth-Diagnostics%E2%80%99-POSLUMA%C2%AE-Flotufolastat-F-18-Injection-First-Radiohybrid-PSMA-targeted-PET-Imaging-Agent-for-Prostate-Cancer