To further understand why obesity or overweight increases lung carcinogenesis, we examined overweight- or obesity-associated changes in cellular signaling molecules, including janus kinase (JAK), signal transducers and activator of transcription 3 (STAT3), protein kinase B (Akt), mammalian target of rapamycin (mTOR), nuclear factor-κB (NF-κB) and cyclin D1 at 21 week point after induction in a urethane-induced lung carcinogenic model by Western blot analyses. The gene discussed is CCND1; the disease is obesity due to melanocortin 4 receptor deficiency.