Cancer caused a total of 7.6 million deaths each year, which is approximately 13% of deaths worldwide. Lung cancer being the most common type, accounts for 1.37 million deaths. But what are the main factors that cause this type of cancer and what can be done to prevent the growing number of deaths? Lung cancer can be defined as an uncontrolled growth of abnormal cells in one or both of an organism's lungs. These abnormal cells divide and multiply to create unhealthy tissue or tumors within the lungs. These tumors interfere with the lungs' ability to supply oxygen to the body. Although lung cancer can start within the lungs, it can also start in other parts of the body. When cancer starts inside the lungs it is called primary lung cancer, when cancer starts elsewhere in the body and spreads to the lungs it is called secondary lung cancer. These two different origins of cancer make the treatments and symptoms very similar, although primary lung cancer is the leading cause of lung cancer death worldwide. Lung cancer can be further divided into types and stages of development to determine the severity of the disease. , there are different types of lung cancer and four stages of development. The two main types of lung cancer include non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). According to the American Cancer Association, 85% of lung cancers are non-small cell lung cancers, while small cell lung cancer occurs less frequently with the remaining 15% of lung cancers. However, there are several subtypes of NSCLC. The most common include: squamous cell (epidermoid) carcinoma, adenocarcinoma, and large cell carcinoma. The subtypes of NSCLC ...... middle of the paper ...... cer Society. Np, nd Web. April 25, 2014. “Lung Cancer.” Lung cancer basics. Mayo Clinic, n.d. Web. April 27, 2014. “Lung Cancer Fact Sheet – American Lung Association.” American Lung Association. American Lung Association, n.d. Web. April 26, 2014. “Lung Cancer.” Lung cancer. Istituto Superiore di Sanità, nd Web. 26 April 2014. "Lung cancer: treatment and cure". WebMD. WebMD and Web. April 27, 2014. “Lymph node.” Wikipedia. Wikimedia Foundation, April 27, 2014. Web. April 27, 2014."Radon and cancer - National Cancer Institute." Radon and cancer - National Cancer Institute. National Cancer Institute, n.d. Web. April 27, 2014."Smoking." - National Cancer Institute. Np, nd Web. April 27, 2014."What is being done to protect people from the dangers of smoking?" What is being done to protect people from the risks of smoking? American Cancer Society, nd Web. 27 April. 2014.