Cancer, which causes about 13% of all deaths worldwide, is a group of diseases in which cells are:
1. aggressive - grow and divide without respect to normal limits,
2. invasive - invade and destroy adjacent tissues, and
3. sometimes metastatic - spread to other locations in the body.
These three malignant properties of cancers differentiate them from benign tumors, which are self-limited in their growth and do not invade or metastasize (although some benign tumor types are capable of becoming malignant).
CAUSES OF CANCER
Cancer may be caused by:
- Chemical carcinogens such as tobacco smoke and alcohol
- Ionizing radiation such as radon gas and UV rays from the sun
- Ifectious diseases associated with viruses like human papillomavirus, hepatitis B and hepatitis C virus, Epstein-Barr virus, and human T-lymphotropic virus
- Hormonal imbalances
- Immune system dysfunction like HIV
Other cancer-promoting genetic abnormalities may be randomly acquired through errors in DNA replication, or are inherited, and thus present in all cells from birth. Complex interactions between carcinogens and the host genome may explain why only some develop cancer after exposure to a known carcinogen. New aspects of the genetics of cancer pathogenesis, such as DNA methylation, and microRNAs are increasingly being recognized as important.
SIGNS AND SYMPTOMS
Roughly, cancer symptoms can be divided into three groups:
- Local symptoms: unusual lumps or swelling (tumor), hemorrhage (bleeding), pain and/or ulceration. Compression of surrounding tissues may cause symptoms such as jaundice.
- Symptoms of metastasis (spreading): enlarged lymph nodes, cough and hemoptysis, hepatomegaly (enlarged liver), bone pain, fracture of affected bones and neurological symptoms. Although advanced cancer may cause pain, it is often not the first symptom.
- 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 symptom in the above list can be caused by a variety of conditions (a list of which is referred to as the differential diagnosis). Cancer may be a common or uncommon cause of each item.
Once diagnosed, cancer is usually treated with a combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for different varieties of cancer. There has been significant progress in the development of targeted therapy drugs that act specifically on detectable molecular abnormalities in certain tumors, and which minimize damage to normal cells. Cancer may be treated by:
- Radiation therapy
- Targeted therapies
- Hormonal therapy
- Symptom control
Cancer has a reputation for being a deadly disease. While this certainly applies to certain particular types, this is increasingly being overturned by advances in medical care. Some types of cancer have a prognosis that is substantially better than nonmalignant diseases such as heart failure and stroke.
Cancer patients, for the first time in the history of oncology, are visibly returning to the athletic arena and workplace. Patients are living longer with either quiescent persistent disease or even complete, durable remissions.
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