APLN and neoplasm: Various apelin peptides can stimulate tumor growth and proliferation of many types of cancer cells, including cholangiocarcinoma (CAA) (Hall et al., 2017), non-small cell lung cancer (NSCLC) (Berta et al., 2010), gastric cancer (Feng et al., 2016), prostate cancer (Tekin et al., 2014), ovarian cancer (Hoffmann et al., 2017), and oral squamous cell carcinoma (Heo et al., 2012).