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

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

References

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. https://www.eurekalert.org/news-releases/976400

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