BMP6 and squamous cell carcinoma: We consider that the exclusion of squamous cell carcinomas in this study partially contributed to the identification of these two biomarkers because analyses of the TCGA dataset suggested that six genes identified through the analyses of cohort 1 and cohort 2a did not have prognostic impact (OLFM1 and NFASC) or had opposite prognostic implications (BMP6, KCNK3, PEG3, and TNXB) in squamous cell carcinomas, as shown in Supplementary Fig. S6.