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Cancer (medical term: malignant neoplasm) is a class of diseases in which a group of cells display uncontrolled growth (division beyond the normal limits), invasion (intrusion on and destruction of adjacent tissues), and sometimes metastasis (spread to other locations in the body via lymph or blood). These three malignant properties of cancers differentiate them from benign tumors, which are self-limited, do not invade or metastasize. Most cancers form a tumor but some, like leukemia, do not. The branch of medicine concerned with the study, diagnosis, treatment, and prevention of cancer is oncology. Cancer may affect people at all ages, even foetus, but the risk for most varieties increases with age. Cancer causes about 13% of all deaths. According to the American Cancer Society, 7.6 million people died from cancer in the world during 2007.Cancers can affect all animals. Importance of World Cancer Day Cancer is a leading cause of death around the world. World Health Organisation (WHO) estimates that 84 million people will die of cancer between 2005 and 2015 without intervention. World Cancer Day is marked on 4th February to raise awareness of cancer and to encourage its prevention, detection, and treatment. It is led by the International Union against Cancer, a global consortium of more than 280 cancer-fighting organizations in over 90 countries. World Cancer Day targets the public through global communications marking, and encourages policy makers and UICC member organizations to make cancer a political priority. Symptoms Cancer is a group of diseases that may cause almost any sign or symptom. The signs and symptoms will depend on where the cancer is, how big it is, and how much it affects nearby organs or tissues. If a cancer has spread (metastasized), symptoms may appear in different parts of the body. As a cancer grows, it can begin to push on nearby organs, blood vessels, and nerves. This pressure creates some of the signs and symptoms of cancer. If the cancer is in a critical area, such as certain parts of the brain, even the smallest tumor can cause early symptoms. But sometimes cancer starts in places where it will not cause any symptoms until it has grown quite large. Pancreas cancers, for example, do not usually grow large enough to be felt from the outside of the body. Some pancreatic cancers do not cause symptoms until they begin to grow around nearby nerves (this causes a backache). Others grow around the bile duct and block the flow of bile. This causes a yellowing of the eyes and skin called jaundice. By the time a pancreatic cancer causes these signs or symptoms, it is usually in an advanced stage. This means it has grown and spread beyond the place it started – the pancreas. A cancer may also cause symptoms like fever, extreme tiredness (fatigue), or weight loss. This may be because, cancer cells use up much of the body’s energy supply, or they may release substances that change the way the body makes energy from food. Or the cancer may cause the immune system to react in ways that produce these symptoms. Sometimes, cancer cells release substances into the bloodstream that cause symptoms which are not usually linked to cancer. For example, some cancers of the pancreas can release substances which cause blood clots in veins of the legs. Some lung cancers make hormone-like substances that raise blood calcium levels. This affects nerves and muscles, making the person feel weak and dizzy. Treatments Experimental cancer treatments are medical therapies intended or claimed to treat cancer (see also tumor) by improving on, supplementing or replacing conventional methods (surgery, chemotherapy, radiation, and immunotherapy). Bacterial treatments Chemotherapeutic drugs have a hard time penetrating tumors to kill them at their core because these cells may lack a good blood supply. Researchers have been using anaerobic bacteria, such as Clostridium novyi, to consume the interior of oxygen-poor tumours. These should then die when they come in contact with the tumour's oxygenated sides, meaning they would be harmless to the rest of the body. A major problem has been that bacteria don't consume all parts of the malignant tissue. However combining the therapy with chemotherapeutic treatments can help to solve this problem. Radiation Therapy Radiation therapy is a process that precisely sends high levels of radiation directly to the cancer cells. Radiation done after surgery can kill cancer cells that may not be seen during surgery There are various ways to deliver radiation therapy. However, external radiation is the usual type that is used for treatment of breast cancer.