Abstract
Vaccine-associated lymphadenopathy (VAL) is a common finding on 18F-FDG PET/CT examinations after coronavirus disease 2019 (COVID-19) vaccination. However, data regarding VAL on 18F-rhPSMA-7.3-ligand PET are currently lacking. This study assesses the prevalence, temporal response to vaccination, and characteristics of VAL. Methods: Two hundred thirty-three consecutive vaccinated and 41 unvaccinated patients with confirmed prostate cancer who underwent 18F-rhPSMA-7.3 PET/CT were retrospectively analyzed. Size and uptake of the axillary lymph nodes were measured. Ratios of SUVmax of ipsilateral to contralateral axillary lymph node (SUVratio) were determined. The characteristics of SUVratio in respect to the duration of PSMA avidity in the axillary lymph node after COVID-19 vaccination was analyzed. Results: The prevalence of VAL on 18F-rhPSMA-7.3 PET was 45%. Up to a period of 8 wk after the last COVID-19 vaccination, SUVratio was positive (2.05 ± 0.17). Thereafter, SUVratio dropped significantly (1.35 ± 0.09) and approached the value of unvaccinated group (1.1 ± 0.2). SUVratio of metastatic axillary lymph nodes was very high (>11) and can be easily detected visually or semiquantitatively. In 3 patients, we observed suspected development and consecutively confirmed involving metastasis of axillary lymph node with SUVratio between 4.0 to 6.6. Correlation between SUVratio and lymph node size (r = 0.93, P < 0.0001) and lymph node size and duration after vaccine (r = -0.88, P < 0.0008) was found. Conclusion: Increased uptake of the PSMA ligand 18F-rhPSMA-7.3 by axillary lymph nodes is common after COVID-19 vaccination and can persist for 8 wk. This finding should be considered in the interpretation of 18F-rhPSMA-7.3 PET/CT examinations.
Highlights
In times of global pandemic of Coronavirus disease 2019 (COVID-19) infections and rapidly increasing vaccinated population, Vaccine-Associated Lymphadenopathy (VAL) in axillary or supraclavicular lymph nodes ipsilateral to the vaccination site on 18F-FDG examinations was increasingly observed [1-6]
The frequency of positive axillary lymph nodes on PSMA-ligand PET/CT examinations in our series is comparable to recently published data for 18F-FDG PET/CT examinations following COVID-19 vaccinations [1-5,13,17]
We only studied patients imaged with 18F-rhPSMA-7.3, which is currently in late-stage clinical trials for prostate cancer imaging
Summary
In times of global pandemic of Coronavirus disease 2019 (COVID-19) infections and rapidly increasing vaccinated population, Vaccine-Associated Lymphadenopathy (VAL) in axillary or supraclavicular lymph nodes ipsilateral to the vaccination site on 18F-FDG examinations was increasingly observed [1-6]. Ipsilateral axillary lymphadenopathy following intramuscular vaccine has been observed with seasonal and H1N1 influenza and human papilloma virus vaccines [7-10]. These findings can impede interpretation of PET imaging, which poses an additional challenge for the workflow in nuclear medicine departments during the pandemic [11,12]. The recognition of false-positive results is crucial to avoid unnecessary surgical re-exploration or medical therapies. This has been recognized by multidisciplinary recommendations of the scientific expert panel [13]. Given the recent approval of two PSMA imaging agents and the high incidence and prevalence of prostate cancer, the most common malignancy in men, it is very likely that many men will undergo PSMA PET imaging after a recent COVID-19 vaccination
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