Cancer is a group of diseases characterized by uncontrolled cell division and the ability of these cells to invade other tissues and spread to other areas of the body where the cells are not normally located (metastasis). Cancer is caused by damage to DNA (genetic material) through genetic and environmental factors, leading to aberrant growth regulation of cells.
Cell multiplication (proliferation) is a normal physiologic process that occurs in almost all tissues and under many circumstances, such as response to injury, immune responses, or to replace cells that have died or have been shed as a part of their lifecycle (in tissues such as skin or the mucous membranes of the digestive tract). Normally the balance between proliferation and cell death is tightly regulated to ensure the integrity of organs and tissues. Mutations in DNA that lead to cancer appear to disrupt these orderly processes.
The uncontrolled and often rapid proliferation of cells can lead to either a benign tumor or a malignant tumor (cancer). Benign tumors do not spread to other parts of the body or invade other tissues, and they are rarely a threat to life. Malignant tumors can invade other organs, spread to distant locations (metastasize) and become life-threatening.
Signs and symptoms
While advanced cancer may cause pain, it is not always the first symptom. Roughly, cancer symptoms can be divided into three groups:
Local symptoms: unusual swelling (tumor in Latin means swelling), hemorrhage (bleeding), ulceration or jaundice.
Symptoms of metastasis (spreading): enlarged lymph nodes, cough and hemoptysis, hepatomegaly (enlarged liver), bone pain, fracture of affected bones and neurological symptoms.
Systemic symptoms: weight loss, poor appetite and cachexia (wasting), excessive sweating (night sweats), anemia, and specific paraneoplastic phenomena, i.e. specific conditions that are due to an active cancer, such as thrombosis or hormonal changes.
Every single item in the above list has a substantial differential diagnosis (it may be associated with unrelated diseases). Often, cancer is an unexpected finding during investigation for much more common symptoms, while others are diagnosed through screening.
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