What is Cancer?
Cancer is a class of diseases characterized by
out-of-control cell growth. There are over 100 different types of cancer, and
each is classified by the type of cell that is initially affected.
Cancer harms the body when altered cells divide
uncontrollably to form lumps or masses of tissue called tumors (except in the
case of leukemia where cancer prohibits normal blood function by abnormal cell
division in the blood stream). Tumors can grow and interfere with the
digestive, nervous, and circulatory systems, and they can release hormones that
alter body function. Tumors that stay in one spot and demonstrate limited
growth are generally considered to be benign.
More dangerous, or malignant, tumors form when two things
occur:
a cancerous cell manages to move throughout the body using
the blood or lymphatic systems, destroying healthy tissue in a process called
invasion
that cell manages to divide and grow, making new blood
vessels to feed itself in a process called angiogenesis.
When a tumor successfully spreads to other parts of the body
and grows, invading and destroying other healthy tissues, it is said to have
metastasized. This process itself is called metastasis, and the result is a
serious condition that is very difficult to treat.
According to the American Cancer Society, Cancer is the
second most common cause of death in the US and accounts for nearly 1 of every
4 deaths. The World Health Organisation estimates that, worldwide, there were
14 million new cancer cases and 8.2 million cancer-related deaths in 2012
(their most recent data).
Individual types of cancer
There are said to be over 200 different types of cancer. We
have the following common cancer types covered in individual Knowledge Center
articles:
How cancer spreadsNurse holding up board with 'cancer'
written on
Scientists reported in Nature Communications (October 2012
issue) that they have discovered an important clue as to why cancer cells
spread. It has something to do with their adhesion (stickiness) properties.
Certain molecular interactions between cells and the scaffolding that holds
them in place (extracellular matrix) cause them to become unstuck at the
original tumor site, they become dislodged, move on and then reattach
themselves at a new site.
The researchers say this discovery is important because
cancer mortality is mainly due to metastatic tumors, those that grow from cells
that have traveled from their original site to another part of the body. These
are called secondary tumors. Only 10% of cancer deaths are caused by the primary
tumors.
The scientists, from the Massachusetts Institute of
Technology, say that finding a way to stop cancer cells from sticking to new
sites could interfere with metastatic disease, and halt the growth of secondary
tumors.
Malignant cells are more agile than non-malignant ones
Scientists from the Physical Sciences-Oncology Centers, USA,
reported in the journal Scientific Reports (April 2013 issue) that malignant
cells are much “nimbler” than non-malignant ones. Malignant cells can pass more
easily through smaller gaps, as well as applying a much greater force on their
environment compared to other cells.
Professor Robert Austin and team created a new catalogue of
the physical and chemical features of cancerous cells with over 100 scientists
from 20 different centers across the United States.
The authors believe their catalogue will help oncologists
detect cancerous cells in patients early on, thus preventing the spread of the
disease to other parts of the body.
Prof. Austin said "By bringing together different types
of experimental expertise to systematically compare metastatic and
non-metastatic cells, we have advanced our knowledge of how metastasis
occurs."
Causes of cancer
Cancer is ultimately the result of cells that uncontrollably
grow and do not die. Normal cells in the body follow an orderly path of growth,
division, and death. Programmed cell death is called apoptosis, and when this
process breaks down, cancer begins to form. Unlike regular cells, cancer cells
do not experience programmatic death and instead continue to grow and divide.
This leads to a mass of abnormal cells that grows out of control.
Genes - the DNA type
Cells can experience uncontrolled growth if there are
mutations to DNA, and therefore, alterations to the genes involved in cell
division. Four key types of gene are responsible for the cell division process:
oncogenes tell cells when to divide, tumor suppressor genes tell cells when not
to divide, suicide genes control apoptosis and tell the cell to kill itself if
something goes wrong, and DNA-repair genes instruct a cell to repair damaged
DNA.
Cancer occurs when a cell's gene mutations make the cell
unable to correct DNA damage and unable to commit suicide. Similarly, cancer is
a result of mutations that inhibit oncogene and tumor suppressor gene function,
leading to uncontrollable cell growth.
Carcinogens
Carcinogens are a class of substances that are directly
responsible for damaging DNA, promoting or aiding cancer. Tobacco, asbestos,
arsenic, radiation such as gamma and x-rays, the sun, and compounds in car
exhaust fumes are all examples of carcinogens. When our bodies are exposed to
carcinogens, free radicals are formed that try to steal electrons from other
molecules in the body. Theses free radicals damage cells and affect their
ability to function normally.
Genes - the family type
Cancer can be the result of a genetic predisposition that is
inherited from family members. It is possible to be born with certain genetic
mutations or a fault in a gene that makes one statistically more likely to
develop cancer later in life.
Cancer and other medical factors
As we age, there is an increase in the number of possible
cancer-causing mutations in our DNA. This makes age an important risk factor
for cancer. Several viruses have also been linked to cancer such as: human
papillomavirus (a cause of cervical cancer), hepatitis B and C (causes of liver
cancer), and Epstein-Barr virus (a cause of some childhood cancers). Human
immunodeficiency virus (HIV) - and anything else that suppresses or weakens the
immune system - inhibits the body's ability to fight infections and increases
the chance of developing cancer.
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