2.1. Differential Expression of SULF1 and SULF2 mRNAs in 32 TCGA Studies

RNA-seq data and clinical information of 9160 patients enrolled in 32 cancer studies conducted by the Cancer Genome Atlas (TCGA) consortium (portal.gdc.cancer.gov, accessed on 26 February 2022) and corresponding non-disease tissues from the Genotype-Tissue Expression (GTEx) project (gtexportal.org/home, accessed on 26 February 2021) were downloaded from UCSC-Xena on 26 February 2021 (xenabrowser.net/datapages, accessed on 26 February 2021); SULF1 and SULF2 mRNA was quantified as log₂(RSEM counts+1) in both datasets. For the differential expression analysis, we selected 14 TCGA cancer studies with n > 10 of paired tumor and normal tissues (Table 1) and we used a Wilcoxon rank sum test to compare paired tumor and non-tumor tissues, where the log₂-fold change (|Log₂FC|) > 1 and the false discovery rate (FDR) < 0.05 across studies were considered as statistically significant. SULF1 and SULF2 mRNA expression was further compared by Wilcoxon rank sum test between unpaired tumor tissues of 24 cancer studies and corresponding non-disease tissues of the same organs reported in GTEx (Supplemental Table S1A).