Cellular RNA was isolated using the RNeasy Mini Kit (QIAGEN) according to the manufacturer's instructions. Total RNA was isolated from tumor tissues using TRIzol (Invitrogen) following the manufacturer's protocol. The RNA quality was assessed using a Bioanalyzer 2100 System (Agilent Technologies, Santa Clara, CA, USA). RNA concentration was measured using a NanoDrop ND-2000 (Thermo Fisher Scientific). The cDNA libraries were constructed using the QuantSeq 3′ mRNA-Seq Library Prep Kit (Lexogen, Inc., Vienna, Austria) and sequenced on a NextSeq 500 (Illumina Inc., San Diego, CA, USA) to generate single-end 75 bp reads according to the manufacturer's instructions.