Lung cancer is a disease caused by abnormal and harmful cell growth in tissues of the lung. The main types of lung cancer are small-cell lung carcinoma (SCLC), also called oat cell cancer, and non-small-cell lung carcinoma (NSCLC). The most common symptoms of lung cancer include coughing, coughing up blood, weight loss, and shortness of breath. Common treatments include surgery, chemotherapy, and radiotherapy. NSCLC is sometimes treated with surgery, whereas SCLC usually responds better to chemotherapy and radiotherapy. In the premise of Breaking Bad, the protagonist, Walter White finds out that he is diagnosed with lung cancer, thus culminating the events of him deciding to cook methamphetamine in order to secure his family's future before he dies. The cancer also symbolizes Walt's decaying loss in his life, and contributing to his re-birth from Walter White to Heisenberg.
Cancer develops following genetic damage to DNA. This genetic damage affects the normal functions of the cell, including cell proliferation, programmed cell death (apoptosis) and DNA repair. As more damage accumulates, the risk of cancer increases. It is possible that Walter White's cause of cancer was through "Radon gas". Radon is a colorless and odorless gas generated by the breakdown of radioactive radium, which in turn is the decay product of uranium. The radiation decay products ionize genetic material which possibly caused a mutation in Walt. According to Skyler's theory of Walt's cancer, 20 years ago when Walt worked at an application lab and his involvement in chemicals, and the fact that Walt would complain about not having the right kind of ventilation hood ("Cancer Man").
- Werner Karl Heisenberg (1901-1976), the physicist and namesake of Walter White's alter ego, died of kidney and gall bladder cancer.