We performed quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis of CCND1, MMP9, HIF1A, BCL3, SOCS1, and SOCS3, which are known STAT3 target genes in breast cancer development27–29, and found that knockout of TMEM25 increased transcription of these genes (Fig. 3c), indicating that TMEM25 indeed functions as an inhibitor of STAT3 signaling. Here, TMEM25 is linked to breast cancer.