In MDA-MB-231 breast cancer cells, proliferation did not change significantly after 24 h of treatment with leptin (Fig. 1C) and decreased significantly by 11% (P=0.023) and 26% (P<0.001) after 48 h of treatment with 400 and 800 ng/ml (P<0.001) of leptin, respectively, compared with the untreated control (Fig. 1D). Here, LEP is linked to breast cancer.