Nowadays, it is a well-known fact that nicotine and tobacco cause cancer. However, it is important to understand why this is the case as well. The main reason why this occurs is because nicotine is linked to a process known as epithelial-mesenchymal transition (EMT). This is involved in the development of malignant cell growth. Moreover, nicotine interacts with the tumor suppressor CHK2, undermining its defense against cancer. Finally, nicotine can speed up cell growth and reduce the effect of cancer treatments.