JAK2 and cancer: Cotreatment with leptin and adipose tissue-derived fibroblast growth factor-2 (FGF2) was reported to induce the malignant transformation of breast epithelial MCF-10A cells, and this effect was found to be attenuated by ruxolitinib and AG490, two separate inhibitors of Jak2, which is downstream of the leptin receptor, suggesting the critical interplay of leptin, leptin receptor and Jak2 in cancer progression [57].