Background/Aim: L-type amino acid transporter 1 (LAT1) is highly expressed in various human cancers. However, the clinicopathological significance of LAT1 and 4F2 cell surface antigen (4F2hc) in patients with colorectal cancer (CRC) is unknown. The aim of this study was to clarify the prognostic significance of LAT1 expression in CRC patients who underwent surgical resection. Materials and Methods: Samples from one hundred and forty-seven patients were examined by immunohistochemistry. The expression of LAT1 and 4F2hc, and the Ki-67 labeling index were assessed using resected tumor specimens. Results: The positive expression of LAT1 and 4F2c was 80% (118/147) and 58% (86/147) (p<0.01), respectively. The expression of LAT1 was identified as an independent significant marker linked to worse prognosis in patients with CRC, and was correlated with tumor cell proliferation, tumor aggressiveness, and metastasis. Moreover, LAT1 was closely associated with the expression of 4F2hc and phosphorylation of the mTOR pathway. Conclusion: LAT1 is a significant molecular marker used to predict prognosis after surgical resection of CRC patients.Colorectal cancer (CRC) is one of the major neoplasms that cause cancer-related deaths worldwide. When the initial diagnosis of CRC is made in the advanced stage of the disease, systemic chemotherapy is a suitable treatment in addition to palliative surgery when necessary. Despite recent translational research efforts, there is still no established biomarker to predict prognosis after any treatment.We investigated the clinicopathological significance of L-type amino acid transporter 1 (LAT1) expression within tumor specimens from patients with human neoplasms and confirmed that LAT1 is highly expressed in many types of cancers (1-9). We found that the increased expression of LAT1 is a clear negative marker predicting worse outcomes in some human cancers (2,(4)(5)(6)(7). Although LAT1 works as a membrane transporter of neutral amino acids, 4F2hc (CD98) is required for its function (10). The L-type amino acid transporter consists of several subtypes, such as LAT1, LAT2, LAT3, and LAT4 (1, 3, 10). Recent studies have indicated that LAT1 can be used as a specific marker for malignant lesions, LAT2 is expressed in normal tissues, LAT3 is observed in hormone-producing tumors such as prostate cancer, and the role of LAT4 in tumor growth and progression is unknown (11). It has been established that LAT1 is an important molecule in targeted therapy, and the inhibition of LAT1 contributes to the suppression of tumor growth via the mammalian target of rapamycin (mTOR) pathway (8, 9). The protein expression of LAT1 has been clinically proven to be different according to the histological subtype, and its overexpression is closely linked to tumor proliferation, angiogenesis, and metastasis (2-9). Little is known about the prognostic significance of LAT1 expression in patients with CRC; however, Hayase et al. recently reported that LAT1 was highly expressed in 72.4% of CRC patients, and its up-2535