Molecular imaging PET-CT in oncologic patients with unsuspected asymptomatic infection with SARS-CoV-2. The Spanish experience (Delta and Omicron variants)

Introduction: The aim of this study was to analyze the incidence of suspicious imaging findings of COVID-19 (Delta and Omicron variants) in PET/CT performed in asymptomatic patients referred to our Department with oncologic indications.

Methods: We analyzed retrospectively the PET-CT scans performed in a tertiary center between March-2020 to January 2022. A number of 3400 patients were evaluated for types of cancer during their oncologic protocol. Inclusion criteria: confirmed cancer, indication for PET-CT in initial staging, follow-up or monitoring of the treatment response. Exclusion criteria: none of these patients were symptomatic for an acute respiratory disease and all of them passed through an epidemiologic screening including : clinical data, information about a possible contact with an infected person, travel in known COVID–19 areas.

Results: Suspicious metabolic COVID-19 lung findings were present in 195 of 3400 patients (5.7%). The most frequent primary was lung cancer (44%), lymphoma (19%), breast cancer (16%) and other tumors in 21% of cases. We observed preferently these findings in FDG scans (Figure 1) but also in 68Ga-DOTATOC (3 cases) and 18F-Fluoro-choline (8 cases) (Figure 2). The range of SUV max in the lung lesions was 3-6 and the most frequent metabolic pattern was heterogeneus uptake, mainly subpleurally in both lungs. Chest CT COVID-19 findings were observed in 83% of the patients, and 27% had normal CT. 55 of the 195 patients were confirmed as presenting SARS-CoV-2 infection with RT-PCR. In the remaining, it was not possible to confirm the presence of COVID-19. Since December 2021 we detected the metabolic pattern correlated with the presently dominant Omicron strain (symmetric FDG uptake throughout the nasopharynx, oropharynx and tonsils with or without associated FDG-avid cervical lymphadenopathy) in 15/300 cases (5%)

Conclusions: The SARS-CoV-2 viral infection in asymptomatic PET-CT cancer patients is a rare possibility, but it represents a challenging scenario both for the diagnosis and also regarding the epidemiologic context, specially wit Omicron variant. Our results confirm that the prevalence of SARS-CoV-2 infection is higher due to the relevant proportion of asymptomatic patients, some of them with lung disease, which can be diagnosed in a presymptomatic phase based on the incidental molecular imaging findings in procedures performed for completely different clinical indications.

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