Evaluation of the Expression of Small Extracellular Vesicle Markers and Their Cargo in Treatment-Naïve Retinoblastoma Tumor Tissues.

Purpose: To evaluate the expression of small extracellular vesicle (sEV)-specific markers in retinoblastoma (RB) tumor tissue and to identify the RB-specific extracellular cargo as biomarker. Methods: Twenty-five treatment-naïve, unilateral RB were included in the study from ophthalmic pathology achieves during January 2020 to December 2022. Demographics, histomorphology, and immunohistochemical analysis were performed on all the samples. The expression of the immunomarkers was graded as faint (+), moderate (++), or marked (+++) compared with immunohistochemistry controls. Results: In the 25 enucleated RB eyes, CD63 (n = 11 [44%]) and TSG101 (n = 23 [92%]) were more prominently expressed sEV markers in the tumor. CD81 was the least expressed. Of the sEV cargo, HIF1a (n = 22, 88%) followed by KAT2B (n = 21 [84%]) showed increased expression in tumor cells with no expression in normal retina. Vascular endothelial growth factor A was seen in 48% of cases and was expressed in normal retina. All the markers showed heterogenous expression in the tumor. Conclusions: Although sEV markers are expressed in tumor microenvironment, their expression is heterogenous in tumors. Of the EV markers, tetraspanin CD63 was predominantly expressed in tumor tissues as compared with CD9 and CD81. Among the previously identified EV cargo, HIF1a and KAT2B were found to be expressed in RB tumors, indicating their potential as biomarkers. Translational Relevance: KAT2B, previously identified as EV cargo, showed expression in tumor tissue, validating its biomarker potential.