Cancer is a form into groups of diseases in which cells are
aggressive (grow and divide without respect to normal limits), invasive (invade
and break up marching tissues), and 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 don't invade or metastasize
(although some benign tumor types are capable of becoming unfavorable). Cancer
may affect people at all ages, even fetuses, but risk as antidote to the more
common varieties tends to increase 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. Apart from humans, forms of cancer may affect other
animals and plants.
Nearly all cancers are caused by abnormalities in the genetic
material of the transformed cells. These abnormalities may be owing to the personal
estate 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 every
part of cells from birth. Complex interactions between carcinogens and the host
genome buy cancer 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 weighty.
Genetic abnormalities found in cancer typically affect two
general classes of genes. Cancer-promoting oncogenes are often activated in cancer
cells, giving those cells new properties, such as hyperactive shooting and division,
protection against programmed cell death, loss of respect for normal series 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, 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 subsist able to 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.
