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Because cancer-associated fibroblasts are central to tumor progression and therapy response, FAPI PET is increasingly explored in neuroendocrine neoplasms (NENs). This review assesses biological rationale, current evidence, and possible clinical applications of FAPI PET for imaging and managing NENs.",{"@graph":69,"@context":123},[70,84,106],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":35,"@type":76,"position":81},"https://docshare.wps.com/document/healthcare/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/fapi-a-solution-to-all-what-about-nens/351948/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/fapi-a-solution-to-all-what-about-nens/351948.png","ImageObject",300,407,{"name":92,"@type":93},"Blitz","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-28","2026-09-22",true,{"@type":102,"interactionType":103,"userInteractionCount":105},"InteractionCounter",{"@type":104},"ViewAction",13,{"@type":107,"mainEntity":108},"FAQPage",[109,115,119],{"name":110,"@type":111,"acceptedAnswer":112},"What is FAPI PET and what does it target in tumors?","Question",{"text":113,"@type":114},"FAPI PET targets fibroblast activation protein (FAP) expressed on cancer-associated fibroblasts, enabling visualization of the tumor stroma rather than the tumor cells themselves.","Answer",{"name":116,"@type":111,"acceptedAnswer":117},"Why is FAPI PET considered useful in tumors with low [18F]FDG avidity?",{"text":118,"@type":114},"FAPI PET exploits FAP overexpression on CAFs, providing high tumor-to-background contrast and improved lesion detection even when [18F]FDG PET has limited uptake.",{"name":120,"@type":111,"acceptedAnswer":121},"How are neuroendocrine neoplasms (NENs) classified in the review?",{"text":122,"@type":114},"NENs span well-differentiated neuroendocrine tumors (NETs) with a more indolent course and poorly differentiated neuroendocrine carcinomas (NECs) that are more aggressive and have worse prognosis.","https://schema.org",{"og:url":83,"og:type":125,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":127,"canonical":83},"index,follow",{"doc_id":129,"site_id":62},351948,1790126482,{"code":4,"msg":5,"data":132},{"doc_id":129,"user_id":133,"nickname":92,"user_avatar":134,"doc_module":4,"category_id":34,"category_name":35,"doc_title":65,"doc_description":67,"doc_content":135,"file_id":136,"file_url":137,"file_type":138,"file_size":139,"view_count":105,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":140,"language":141,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":142,"faqs":143,"seo_title":144,"seo_description":67,"update_tm":145,"read_time":146},24464137899374,"https://us-avatar.wpscdn.com/davatar_3d24733baf745e90a7e4bdd5f77d97b2","Ekmekcioglu etal. EJNMMI Reports (2026) 10:35 EJNMMI Reports  \n[https://doi.org/10.1186/s41824-026-00321-8](https://doi.org/10.1186/s41824-026-00321-8)  \nREVIEW Open Access  \nFAPI: a solution to all, what about NENs?  \nOzgul Ekmekcioglu 1*, Filiz Celik2, Simon Hughes3, Meltem Ocak4, Fred Verzijlbergen5, Stefano Fanti6 and Christophe M. Deroose7,8  \n*Correspondence: Ozgul Ekmekcioglu [ozgulek@gmail.com](ozgulek@gmail.com)  \nFull list of author information is available at the end of the article  \nAbstract  \nFibroblast activation protein (FAP)–targeted PET imaging is an emerging technique that images the tumor stroma by targeting cancer-associated fibroblasts, offering high tumor-to-background contrast and improved lesion detection in tumors with low [¹⁸ F]FDG avidity. Given the central role of CAFs in tumor progression and therapy response, FAPI PET has gained interest in neuroendocrine neoplasms (NENs), where stromal imaging may provide complementary information to conventional modalities. This review evaluates the biological rationale, current evidence, and potential clinical role of FAPI PET in the imaging and management of NENs. Keywords FAPI, Neuroendocrine tumors, PET/CT, Fibroblast activation protein  \nIntroduction  \nFibroblast activation protein (FAP) PET imaging represents a novel and increasingly valuable modality in nuclear medicine imaging, distinguished by its targeting of the tumor stroma rather than the tumor cells themselves, in most tumor types (Hirmaset al. 2023). Unlike [18F]FDG PET, which relies on elevated glucose metabolism, FAP PET exploits the overexpression of FAP on cancer-associated fibroblasts (CAFs), a key component of the tumor microenvironment implicated in tumor progression, metastasis, and immune evasion. Radiotracers based on FAP inhibitors (FAPIs) such as [68Ga] Ga-FAPI-46 or [18F]AlF-FAPI-74 have demonstrated high tumor-to-background (TBR) contrast across a wide range of malignancies, including those that exhibit low [18F]FDG avidity, thereby offering superior lesion detectability in selected clinical contexts (Li et al. 2022, Pabst, Kim et al. 2025, Hope et al. 2025).  \nFibroblasts are the predominant stromal cell type within the tumor mesenchyme of many solid malignancies, particularly those of gastrointestinal origin (Kalluri and Zeisberg 2006). A subset of these, known as cancer-associated fibroblasts (CAFs), arise from resident fibroblasts or mesenchymal stem cells that become activated within the tumor microenvironment (TME). CAFs contribute to tumor progression by secreting a variety of signaling molecules, including exosomes, which influence key processes such as cell proliferation, invasion, migration, drug resistance, and metastatic dissemination (Caligiuri 2023). They are thus considered central mediators of tumor aggressiveness. Among  \n© The Author(s) 2026. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit [http://creativecommons.org/l](http://creativecommons.org/l)icenses/by-nc-nd/4.0/.  \nEkmekcioglu et al. EJNMMI Reports (2026) 10:35 Page 2 of 14  \nthese, FAP plays a particu","cbCaioWvYoXfihUu","https://ap.wps.com/l/cbCaioWvYoXfihUu","pdf",1081442,14,"English","# Abstract\n# Introduction\n## FAPI PET imaging principles\n## CAF biology and tumor microenvironment\n# Biological rationale for FAPI PET in NENs\n## NEN classification and clinical context\n## Comparison with SSTR PET","[{\"question\":\"What is FAPI PET and what does it target in tumors?\",\"answer\":\"FAPI PET targets fibroblast activation protein (FAP) expressed on cancer-associated fibroblasts, enabling visualization of the tumor stroma rather than the tumor cells themselves.\"},{\"question\":\"Why is FAPI PET considered useful in tumors with low [18F]FDG avidity?\",\"answer\":\"FAPI PET exploits FAP overexpression on CAFs, providing high tumor-to-background contrast and improved lesion detection even when [18F]FDG PET has limited uptake.\"},{\"question\":\"How are neuroendocrine neoplasms (NENs) classified in the review?\",\"answer\":\"NENs span well-differentiated neuroendocrine tumors (NETs) with a more indolent course and poorly differentiated neuroendocrine carcinomas (NECs) that are more aggressive and have worse prognosis.\"}]","FAPI: a solution to all, what about NENs? | PDF",1790096580,35]