Absolute Lymphocyte Count After COVID-19 Vaccination Is Associated with Vaccine-Induced Hypermetabolic Lymph Nodes on 18F-FDG PET/CT: A Focus in Breast Cancer Care.

We aimed to predict the presence of vaccine-induced hypermetabolic lymph nodes (v-HLNs) on 18F-FDG PET/CT after coronavirus disease 2019 (COVID-19) vaccination and determine their association with lymphocyte counts. Methods: In this retrospective single-center study, we included consecutive patients who underwent 18F-FDG PET/CT imaging after messenger RNA- or viral vector-based COVID-19 vaccination between early March and late April 2021. Demographics, clinical parameters, and absolute lymphocyte count (ALC) were collected, and their association with the presence of v-HLNs in the draining territory was studied by logistic regression. Results: In total, 260 patients were eligible, including 209 (80%) women and 145 (56%) with breast cancer. The median age was 50 y (range, 23-96 y). The messenger RNA vaccine had been given to 233 (90%). Ninety (35%) patients had v-HLNs, with a median SUVmax of 3.7 (range, 2.0-26.3), and 74 (44%) displayed lymphopenia, with a median ALC of 1.4 × 109/L (range, 0.3-18.3 × 109/L). An age of no more than 50 y (odds ratio [OR], 2.2; 95% CI, 1.0-4.5), the absence of lymphopenia (OR, 2.2; 95% CI, 1.1-4.3), and less than a 30-d interval from the last vaccine injection to the 18F-FDG PET/CT (OR, 2.6; 95% CI, 1.3-5.6) were independent factors for v-HLNs on multivariate analysis. In breast cancer patients, the absence of lymphopenia was the only independent factor significantly associated with v-HLNs (OR, 2.9; 95% CI, 1.2-7.4). Conclusion: Patients with a normal ALC after COVID-19 vaccination were more likely to have v-HLNs on 18F-FDG PET/CT, both of which might be associated with a stronger immune response to vaccination.

Metabolic Response by 18F-FDG PET/CT in Metastatic Malignant Struma Ovarii Treated With Targeted Therapies.

Malignant struma ovarii (MSO) is a rare malignant ovarian tumor, histologically identical to differentiated thyroid cancers. Given the rarity of this disease, there are no treatment guidelines, and the place of imaging for response assessment remains controversial. We report a metabolic response assessed by F-FDG PET/CT in a 71-year-old woman with radioiodine-refractory metastatic MSO treated by targeted therapies (first line with lenvatinib and second line with pazopanib). This case of exceptional response also highlights the usefulness of F-FDG PET/CT for therapeutic assessment of targeted drugs in such a rare clinical entity of malignant MSO.