e15138 Background: Colorectal cancer (CRC) is a heterogeneous disease defined by anatomic, functional and molecular differences depending on the primary tumor location (PTL). Several molecular phenotypes have been associated with aggressive behavior, and some of these markers are related with proteoglycans, which in turn show alterations in CRC. Small leucine-rich proteoglycans (SLRPs) are a family of molecules encoded by18 genes that may appear coupled to different glycosaminoglycan chains ––including chondroitin/dermatan or keratan sulphate–– or not, depending on the specific species. They are ubiquitously expressed in extracellular matrices, and it’s been described their role in organ size and shape regulation during embryonic development. This study aims to investigate the expression patterns of SLRPs in CRC depending on the PTL. Methods: A transcriptomic approach was carried out by using qPCR to analyze SLRP core protein transcriptions in 32 tumor specimens and their respective healthy tissue: 12 right-sided & 20 left-sided. When significant differences were detected, immunohistochemical techniques were used to enhance the test. Results: While right-sided (R) CRC displayed significant alterations in 2 genes (biglycan BGN overexpression p = 0.015, osteoglycin OGN underexpression p = 0.048), left-sided (L) showed differences in 5 genes (BGN overexpression p = 0.0019 and underexpression of OGN p = 0.0016, prolargin PRELP p = 0.0049, chondroadherin CHAD p = 0.0180 and podocan PODN p = 0.0061). In L tumors CHAD was the most affected gen underexpressed by 16 times, while in R it was present in only 50% of healthy tissue. Transcripts for opticin and nyctalopin were not detected in most patients regardless of PTL. Lumican, decorin, keratocan, asporin, ECM2, fibromodulin, tsukushi, osteoadherin, osteomodulin, epiphycan and PODN-like 1 were detected with no significant differences compared to healthy tissue. Conclusions: Normal mucosa of the large bowel expresses most SLRP. BGN and OGN seem to be dysregulated in both L and R CRC, but CHAD, PRELP and PODN appear to show differences only in L CRC. These alterations could be related to the interaction with different ligands and modulation of homeostasis.