PPIG and small cell lung carcinoma: Peptidylprolyl isomerase A as one of the most abundant members of cyclophilin (Cyp) family proteins has been reported upregulated in breast cancer (Volker et al., 2018), esophageal cancer (Qi et al., 2008), small cell lung cancer (Campa et al., 2003), colorectal cancer (Wong et al., 2008), pancreatic cancer (Li et al., 2013), melanoma (Caputo et al., 2011), malignant glioblastoma (Sun et al., 2011; Saw et al., 2018), serous ovarian cancer (Qi et al., 2019), and skin cancer (Han et al., 2012).