PPIA and small cell lung carcinoma: Intriguingly, although CsA, the potent inhibitor of cyclophilin A, may induce skin cancer when used in transplantation [89,90,91,92,167,168,169], cyclophilin A has been observed to be upregulated in many solid cancers such as breast cancer, small-cell lung cancer, pancreatic cancer, colorectal cancer, squamous cell carcinoma, and melanoma [53].