Novel PET Radiotracer Reduces False-Positive Tumors After COVID-19 Vaccination


18F-FDG PET/CT detects approximately 73% of tumor lesions, while 68Ga-FAPI finds approximately 94%.

Novel imaging agent 68Ga-FAPI can reduce the number of false-positive positron emission tomography (PET)/computerized tomography (CT) findings among individuals with cancer recently vaccinated against COVID-19, according to the results of a study published in The Journal of Nuclear Medicine.1

The imaging agent can detect lesions without vaccine-related tracer uptake in locoregional lymph nodes that is common with 18F-FDG imaging.1

“This observation is concerning, as vulnerable groups, such as oncologic patients, undergo both regular COVID-19 booster shots and medical imaging,” Tristan Demmert, MD, researcher in the Department of Nuclear Medicine at Essen University Hospital in Essen, Germany, said in a statement. “False positive findings on 18F-FDG PET due to reactive uptake may trigger false management decisions.”1

One of the adverse events of a COVID-19 vaccine is that 18F-FDG, the most used PET imaging agent, is taken up by immune cells responding to the mRNA inflammatory stimulus that is caused by the vaccine. This causes a reactive uptake but does not always indicate that a tumor is present.1

Investigators compared the 2 radiotracers to determine if there was a way to avoid false positives. They included 11 oncologic individuals, from a large perspective imaging registry, who received COVID-19 vaccinations within 6 weeks, had 68Ga-FAPI and 18F-FDG imaging on the same day, and had documentation of tracer uptake in the locoregional lymph nodes.1 Individuals were identified between May 2021 and April 2022.2

Ten individuals received the BNT162b2 vaccine from Pfizer/BioNTech, while 1 received the mRNA1273 vaccine from Moderna). There was a median interval of 19 days before PET/CT.2

Two medicine physicians performed visual readings of the images.1

Investigators found that all patients with 18F-FDG PET/CT had significant lymph node uptake adjacent to the injection site, while none experienced it with 68Ga-FAPI.1

Additionally, 18F-FDG PET/CT detected approximately 73% of tumor lesions, while 68Ga-FAPI detected approximately 94% of all tumor lesions.1

“In patients with suspected tumors in the axillary region, a costly follow-up was often recommended to avoid incorrect patient treatment. According to our results, this could have been prevented by using 68Ga-FAPI, which would have allowed higher tumor detection at the same time,” Demmert said.

“Considering that further booster vaccinations are expected, 68Ga-FAPI could show its potential in avoiding vaccine-related misinterpretations on PET/CT while providing equivalent tumor detection,” he said.1

This could potentially help prevent costly follow-up and false management decisions for individuals with cancer, investigators said.1

They also called for careful consideration of planning PET/CT appointments and vaccinations, because patients are at risk of false positive lymph nodes findings within 6 weeks of vaccination.2

Furthermore, they advised caution about the results, because of lesions not being verified by imaging follow-up and a limited sample size, which makes further investigation necessary.2


1. Novel PET radiotracer reduces number of false-positive cancer findings after COVID-19 vaccination. EurekAlert. News release. January 11, 2023. Accessed January 16, 2023.

2. Demmert TT, Maric I, Pomykala KL, Lueckerath K, et al. Novel 68Ga-FAPI PET/CT offers oncologic staging without COVID-19 vaccine-related pitfalls. J Nucl Med. 2022;jnumed.122.264872. doi:10.2967/jnumed.122.264872

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