Abstract 4631: Multiplex IHC assay to explore regional heterogeneity of FAP and inflammatory cell density in localized prostatic adenocarcinoma
Authors: Pereira Fernanda Caramella , Meeker Alan K. , Pienta Kenneth , Zheng Qizhi , Jones Tracy , Yegnasubramanian Srinivasan , Hicks Jessica L. , Roy Sujayita , De Marzo Angelo M. , Brennen W. Nathaniel 
Published: April 2023

Abstract
Cancer-associated fibroblasts (CAFs) expressing FAP promote tumor growth, invasion and immune suppression. FAP is a molecular imaging target in cancer and its protease activity is a potential anti-cancer drug target. While FAP expression was associated with biochemical recurrence after prostatectomy using tissue microarrays (TMAs)(DOI:10.1158/2767-9764.CRC-21-0183), its expression has not been comprehensively correlated with morphological features of disease aggressiveness beyond grade. 48 cases of localized prostatic adenocarcinoma were used for a multiplex immunohistochemical assay that included FAP, CD45, CD163, p63 and Keratin 8. Each of these markers were individually optimized by single-plex staining and were then performed as an iterative IHC assay (PMID:35188986) and quantification was performed using the HALO image analysis platform (Indica Labs). We developed a second multiplex assay including FAP, vimentin, smooth muscle actin, desmin, CD31, S100, keratin 8 and p63. FAP IHC staining was analytically validated using a series of positive and negative cell lines. In normal appearing (non-inflamed) prostate regions, FAP expression was negative. By contrast, upregulation of FAP was observed in the stromal compartment in regions of chronic inflammation and some proliferative inflammatory atrophy (PIA) lesions. In tumor regions, only 1 case was totally negative for FAP. Except for 2 cases, in which there was focal weak tumor cell staining, all FAP expression was present in the tumor stromal compartment (TSC). The vast majority of FAP expression was associated with Vim+/Des- fibroblasts, which at times were also positive for SMA (Vim+/Des-/SMA+), indicating they are myofibroblasts. There was very infrequent FAP expression associated with M2 macrophages, endothelial cells, nerves and vimentin-negative smooth muscle cells, indicating that the majority of FAP expression occurs in fibroblasts. Preliminary quantitative data using visual estimations of the fraction of TSC expressing FAP (range, 0-80%, mean=35.8%, median=30%, SD=23.7) was not associated with the overall GS/grade group, but was associated with non-organ confined disease. Furthermore, there was a trend towards increased FAP expression in cases showing intraductal carcinoma and large cribriform formation. Ongoing studies are in process to obtain quantitative data by image analysis and to correlate FAP expression with the presence of overall inflammatory cell density and the density of M2 macrophages. Additionally, we will characterize the cases in terms of molecular features including TMPRSS2-ERG status and PTEN genomic status. Future use of these panels will facilitate studies of associations of FAP with clinical outcome, MRI and PET imaging, response to specific treatments and to help characterize FAP as a predictor of response to emerging FAP inhibitors and FAP-targeted prodrugs.
Citation Format: Fernanda Caramella Pereira, Alan K. Meeker, Kenneth Pienta, Qizhi Zheng, Tracy Jones, Srinivasan Yegnasubramanian, Jessica L. Hicks, Sujayita Roy, Angelo M. De Marzo, W. Nathaniel Brennen. Multiplex IHC assay to explore regional heterogeneity of FAP and inflammatory cell density in localized prostatic adenocarcinoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4631.