Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. Not all tumors are cancerous; benign tumors do not spread to other parts of the body. Possible signs and symptoms include a lump, abnormal bleeding, prolonged cough, unexplained weight loss and a change in bowel movements. While these symptoms may indicate cancer, they may have other causes. Over 100 cancers affect humans.
Tobacco use is the cause of about 22% of cancer deaths. Another 10% is due to obesity, poor diet, lack of physical activity and drinking alcohol. Other factors include certain infections, exposure to ionizing radiation and environmental pollutants. In the developing world, nearly 20% of cancers are due to infections such as hepatitis B, hepatitis C, and human papillomavirus.
The most common types of cancer in males are lung cancer, prostate cancer, colorectal cancer, and stomach cancer. In females, the most common types are breast cancer, colorectal cancer, lung cancer, and cervical cancer. If skin cancer other than melanoma were included in total new cancers each year it would account for around 40% of cases.
The risk of cancer increases significantly with age and many cancers occur more commonly in developed countries. Rates are increasing as more people live to old age and lifestyle changes occur in the developing world.
The most commonly diagnosed cancers vary by country, especially for males, with prostate and lung cancers occurring most often. For females, breast and cervical cancers happen most frequently. Although higher-income countries lead the world in cancer incidence, lower-to-middle-income countries present the highest rates of infection-related cancers, such as stomach, liver and cervical cancers.
