Postoperative Spindle Cell Nodule Mimicking Metastatic Lesion With Persistently Increasing 68 Ga-FAPI-04 Uptake After Receiving Personalized Antigen Peptide Tumor Vaccine.

A 59-year-old woman underwent radical surgery and chemotherapy for gastric adenocarcinoma. After the personalized antigen peptide tumor vaccine, a new nodular lesion, in the upper abdomen, was discovered during 68 Ga-FAPI-04 PET/MRI follow-up. To determine possible pseudoprogression, 68 Ga-FAPI-04 PET/MRI was repeated 39 days later, referring to immune PET response criteria in solid tumors. The lesion showed increased 68 Ga-FAPI-04 uptake, whereas uptake in vaccine injection sites decreased, and was ultimately diagnosed as a postoperative spindle cell nodule.