"Nicotine, which is the addictive component of tobacco smoke, is unable to initiate tumorigenesis in humans and rodents; at the same time, nicotine has been shown to promote tumor growth and metastasis by inducing cell cycle progression, epithelial-to-mesenchymal transition (EMT), migration, invasion, angiogenesis, and evasion of apoptosis in a variety of systems (8–13). In addition, nicotine has been shown to induce secretion of growth factors and cytokines altering the physiology of multiple organ systems (8–13). These observations suggest that nicotine likely contributes to the progression and metastasis of tumors that are initiated by tobacco carcinogens."
It basically works as an accelerant, stimulating and encouraging tumor growth and metastasis.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3915512/#S7titl...
"Nicotine, which is the addictive component of tobacco smoke, is unable to initiate tumorigenesis in humans and rodents; at the same time, nicotine has been shown to promote tumor growth and metastasis by inducing cell cycle progression, epithelial-to-mesenchymal transition (EMT), migration, invasion, angiogenesis, and evasion of apoptosis in a variety of systems (8–13). In addition, nicotine has been shown to induce secretion of growth factors and cytokines altering the physiology of multiple organ systems (8–13). These observations suggest that nicotine likely contributes to the progression and metastasis of tumors that are initiated by tobacco carcinogens."