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Summary: Fibrolamellar carcinomas (FLC) are a rare type of primary hepatocellular carcinoma found in younger individuals. FLC are known to have relatively few consistent chromosomal alterations, although a gain of chromosome 1q has been reported. The gene expression of 4 FLC (2 primary FLC and 2 metastatic deposits) were studied using Affymetrix DNA microarray technology (Santa Clara, CA). Selected genes were confirmed by real-time polymerase chain reaction. Relatively few genes were significantly overexpressed—447 genes, case 1; 1298 genes, case 2—corresponding to approximately 0.8% and 2.3%, respectively, of the 56000 transcripts present in the arrays. Of these, 155 genes were overexpressed simultaneously by both tumors. The number of significantly overexpressed genes more than doubled in the 2 metastatic deposits (2777 and 2855 genes compared with 1298 in the primary tumor). Proteins involved in the RAS, MAPK, PIK3, and xenobiotic degradation pathways were commonly overexpressed. Because chromosome 1q is thought to contain an important oncogene, additional attention was focused on this region. Of 114 total genes found overexpressed in common among all primary and metastatic tumors, 11 of 114 genes were located on chromosome 1q: ARF1, CD46, CNIH4, ENSA, FH, NICE-3, PSMB4, RGS2, RGS5, TIMM17A, and UFC1. Primary FLC show overexpression of genes involved in the RAS, MAPK, PIK3, and xenobiotic degradation pathways. Eleven common genes were consistently overexpressed on chromosome 1q among all tumors and metastases and warrant further study as potential oncogenes. [Copyright &y& Elsevier]