Axillary Skin Fibroblast Activation Protein Uptake After Chemo-immunotherapy on PET/CT and SPET/CT: A Mere...

Fibroblast activation protein (FAP) uptake can occur in benign conditions in addition to malignancies. This case series presents the first evidence of diffuse FAP uptake in axillary skin on PET/CT and SPET/CT of 33 patients with progressive solid tumors, referred to peptide-targeted radionuclide therapy after failing prior chemotherapy and/or immunotherapy. Upon physical examination, no significant findings were observed in the axillary regions. We hypothesize that fibroblastic activation may involve sweat glands consequently to systemic therapy, although the reason why the axillary site is favored is not known. Being common in this clinical setting, proper interpretation of this sign is needed.