This enhanced 18F-FAPI-04 uptake may be attributed to the high expression of FAP in the predominant cell population within the tumor stroma of many epithelial malignancies (known as CAFs), combined with the observation that most PMs histopathologically exhibit a pronounced desmoplastic reaction, while the original tumor cells constitute a minority [35], leaving original tumor cells in the minority. Here, FAP is linked to neoplasm.