Challenging Axillary Lymph-Nodes on PET/CT in Cancer Patients throughout Covid-19 Vaccination Era

Background: unexpected detection of axillary lymphadenopathy (AxL) in cancer patients (Pts) represents a real concern during COVID-19 vaccination era. Benign reactions may take place after vaccine inoculation, confounding image interpretation in patients undergoing F-18-FDG, F-18-Choline and Ga-68-DOTATOC PET/CT. It may simulate loco-regional metastases/disease. We assessed PET/CT findings after COVID-19 vaccination in cancer patients and the impact on their management. Methods: we evaluated 333 patients undergoing PET/CT (257 F-18-FDG, 54 F-18-Choline and 23 Ga-68 DOTATOC) scans after first vaccination with mRNA vaccine (Pfizer-BioNTech) (study group; SG). Uptake index (SUVmax) of suspected AxL was defined significant when the ratio was >1.5 as compared to the contralateral lympho-nodal site. Besides, co-registered CT (Co-CT) features of target lymph-nodes were evaluated. Nodes with aggregate imaging positivity were further investigated. Results: overall, the prevalence of apparently positive lymph-nodes on PET scans was 17.1% during vaccination era. 107 Pts of the same setting, who had also undergone PET/CT before COVID-19 pandemic constituted a control group (CG). Only 3 patients of CG showed reactive lymph-nodes with a prevalence of 2.8% (p<0.001 as compared to vaccination era). 84.2% of SG patients exhibited benign characteristics on Co-CT images and only 9 Pts needed additional appraisal. Conclusions: the correct interpretation of images is crucial to avoid unnecessary management changes and to rule out invasive procedures in vaccinated cancer Pts undergoing diagnostics. An accurate anamnestic interview and the precise assessment of lymph-nodes’ CT characteristics, when performing PET/CT, may help for settling any diagnostic hypothesis.