Differences in reporting of side effects between JAK inhibitors were observed, for example, while tofacitinib (JAK1/JAK3 inhibitor) generates cardiovascular and cancer effects as well as gastrointestinal perforations, baricitinib (JAK1/JAK2 inhibitor) caused more embolism and thrombosis, and ruxolitinib (JAK1/JAK2 inhibitor) caused more malignant hematopoietic and skin neoplasia. This evidence concerns the gene JAK1 and cancer.