Cancer
Definition:-
There is no one definition that describes all cancers.
They are a large family of diseases which show features suggestive of
malignancy.
They form a subset of neoplasm. A neoplasm or
tumor is a group of cells that have undergone unregulated growth, and will
often form a mass or lump, but may be distributed diffusely.
Six characteristics of malignancies have been
proposed:
Self-sufficiency in growth signaling in sensitivity
to anti-growth signals evasion of apoptosis enabling of a limitless replicative
potential induction and sustainment of angiogenesis activation of metastasis
and invasion of tissues.
The progression from normal cells to cells
that can form a discernible mass to outright cancer involves multiple steps
known as malignant progression.
Signs and symptoms:-
When cancer begins, it invariably produces no
symptoms. Signs and symptoms only appear as the mass continues to grow or
ulcerates. The findings that result depend on the type and location of the
cancer. Few symptoms are specific, with many of them also frequently occurring
in individuals who have other conditions. Cancer is the new “great imitator”.
Thus it is not uncommon for people diagnosed with cancer to have been treated
for other diseases to which it was assumed their symptoms were due.
Local effects:-
Local symptoms may occur due to the mass of
the tumor or its ulceration. For example, mass effects from lung cancer can
cause blockage of the bronchus resulting in cough or pneumonia; esophageal
cancer can cause narrowing of the esophagus, making it difficult or painful to
swallow; and colorectal cancer may lead to narrowing or blockage in the bowel habits.
Masses in breast or testicals may be easily felt. Ulceration can causes
bleeding which, if it occurs in lungs, will lead to coughing up blood, in the urine,
and in the uterus to vaginal bleeding. Although localized pain may occur in
advanced cancer, the initial swelling is usually painless. Some cancer can
cause buildup of fluid within the chest or abdomen.
Systemic symptoms:-
General symptoms occur due to distant effects
of the cancer that are not related to direct or metastatic spread. These may includes:
unintentional weight loss, fever, being excessively tired, and changes to skin.
Hodgkin disease, leukemia’s, and cancers of liver or kidney can cause a
persistent fever of unknown origin.
Some cancers may cause specific groups of
systematic symptoms, termed paraneoplastic phenomena. Examples include the
appearance of myasthenia gravis in thymoma and clubbing in lung cancer.
Metastasis:-
Cancer can spread from its original site by
local spread, lymphatic spread to original lymph nodes or by blood (haematogenous
spread) to distant sites, known as metastasis. When cancer spread by
haematogenous route, it’s usually spreads all over body. However, cancer”seeds”grow
in certain selected site only (soil)as hypothesized in soil and seed hypothesis
of cancer metastasis. The symptoms of metastatic cancer depend on the location
of tumor, and can include enlarge liver or enlarge spleen, which can be felt in
the abdomen, pain or fracture of affected bones, and neurological symptoms.
Causes:-
The great majority of cancers, some 90-95% of
cases, are due to environment factors. The remaining 5-10% is due to inherited
genetics. Environmental, as used by cancer researchers, means any cause that is
not inherited genetically, such as lifestyle, economic and behavioral factors
that contribute to cancer death include tobacco(25-30%), diet and obesity
(30-35%), infections (15-20%), radiations(both ionizing and nonionizing, up
to 10%),stress, lack of physical activity, and environmental pollutants.
It is nearly impossible to prove what caused a
cancer in any individual, because most cancer has multiple possible causes. For
example, if a person who uses tobacco heavily develops lung cancer, then it was
probably caused by the tobacco use, but since everyone has a small chance of
developing lung cancer as a result of air pollution or radiation, then there is
a small chance that the cancer developed because of air pollution and radiation.
Excepting the rare transmissions that occur with pregnancies and only a
marginal few organ donors, cancer is generally not a transmissible disease.
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