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Cancer in the medical term
(malignant neoplasm) is a class of diseases in which a group of cells display
the traits of uncontrolled growth, invasion and sometimes metastasis. 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.
Cancer may affect people at all
ages, even fetuses, but risk for the more common varieties tends to increase
with age. Cancer causes about 13% of all deaths. According to the American
Cancer Society, in the year of 2007, 7.6 million people died from cancer all
Over the world. Cancers can affect other animals besides humans, and plants,
too.
Nearly all cancers are caused by abnormalities in the genetic material of the
transformed cells. These abnormalities may be due to the effects of carcinogens,
such as tobacco smoke, radiation, chemicals, or infectious agents. 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.
New aspects of the genetics of cancer pathogenesis, such as DNA methylation, and
microRNAs are increasingly being recognized as important.
Genetic abnormalities found in cancer typically affect two general classes of
genes. Cancer-promoting ontogenesis are often activated in cancer cells, giving
those cells new properties, such as hyperactive growth and division, protection
against programmed cell death, loss of respect for normal tissue boundaries, and
the ability to become established in diverse tissue environments. Tumor
suppressor genes are often inactivated in cancer cells, resulting in the loss of
normal functions in those cells, such as accurate DNA replication, control over
the cell cycle, orientation and adhesion within tissues, and interaction with
protective cells of the immune system.
Cancer is usually classified according to the tissue from which the cancerous
cells originate, the primary tumor, as well as the Cancer is usually classified
according to the tissue from which the cancerous cells originate, the primary
tumor, as well as the normal cell type they most resemble. These are location
and histology, respectively. A definitive diagnosis usually requires the
histologic examination of a tissue biopsy specimen by a pathologist, although
the initial indication of malignancy can be symptoms or radiographic imaging
abnormalities. Most cancers can be treated and some cured, depending on the
specific type, location, and stage. 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. The prognosis of
cancer patients is most influenced by the type of cancer, as well as the stage,
or extent of the disease. In addition, histologic grading and the presence of
specific molecular markers can also be useful in establishing prognosis, as well
as in determining individual treatments.
Signs and symptoms
Cancer symptoms can be divided into three type:
1. Local symptoms: unusual lumps or swelling (tumor), hemorrhage
(bleeding), pain and/or ulceration. Compression of surrounding tissues may cause
symptoms such as jaundice (yellowing the eyes and skin).
2. 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.
3. Systemic symptoms: weight loss, poor appetite, fatigue 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.
Treatment
Cancer can be treated by surgery, chemotherapy, radiation therapy,
immunotherapy, monoclonal antibody therapy or other methods. The choice of
therapy depends upon the location and grade of the tumor and the stage of the
disease, as well as the general state of the patient (performance status).
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