Adin ME, Isufi E, Kulon M, et al. - Induction of ipsilateral axillary lymph node reactivity following the receipt of intramuscular coronavirus 2019 (COVID-19) vaccinations may be falsely attributed to malignant abnormality, prompting unwarranted interventions, or it may be falsely attributed to vaccination rather than cancer, potentially delaying cancer care. Researchers aimed at examining Moderna and Pfizer COVID-19 vaccine-related nodal reactivity on ¹⁸F-flurodeoxyglocose (FDG) positron emission tomographic (PET)/computed tomographic (CT) scans. They screened all patients (n = 1,290) who underwent FDG-PET/CT scans at the Yale New Haven Hospital between December 11, 2020 and March 1, 2021, for COVID-19 vaccination. Analysis was performed including 68 patients who received at least 1 dose of COVID-19 vaccine. Observations revealed occurrence of ipsilateral axillary nodal reactivity after the first vaccine dose in 2 patients (5%) and after the second vaccine dose in 7 (26%); 4 patients (57%) after the second dose of the Moderna vaccine and 3 (15%) after the second dose of the Pfizer vaccine. In the Moderna trial, patient survey revealed occurrence of axillary swelling and tenderness in 1,322 (11.6%) patients after the first dose (567 [5%] placebo) and in 1,654 (16%) after the second dose (444 [4.3%] placebo) of vaccine; only unsolicited reactions were recorded in the Pfizer trial. In the present study, nodal enlargement on CT findings was observed in only 5 patients (56%) with nodal reactivity on PET. This cohort showed elevated nodal FDG uptake, presumably from an inflammatory immune response to the vaccine, up to 32 days after vaccination; this harbors the potential risk of mimicking or masking malignant disease. The COVID-19 vaccine should be administered in the axilla contralateral to the previously or potentially involved site among patients with cancer with a propensity for spread to ipsilateral axillary lymph nodes—breast cancer, melanoma, lymphomas. They recommend nuclear medicine technologists to record vaccine site, date, type, and first vs second dose. This cohort much less frequently showed ipsilateral axillary nodal activity after the first vaccine dose and there were more frequently women who developed reactive nodes, an important implication for breast cancer imaging concordant with the statement issued by the Society of Breast Imaging.