Cancer is a group of diseases
involving abnormal cell growth with the potential to invade or spread to other
parts of the body. These contrast with benign tumors, which do not spread.
Possible signs and symptoms include a lump, abnormal bleeding, prolonged cough,
unexplained weight loss, and a change in bowel movements. While these symptoms
may indicate cancer, they can also have other causes. Over 100 types of cancers
affect humans.
The major types of cancer are carcinoma, sarcoma, melanoma, lymphoma,
and leukemia. Carcinomas -- the most commonly diagnosed cancers -- originate in
the skin, lungs, breasts, pancreas, and other organs and glands. Lymphomas are
cancers of lymphocytes. Leukemia is cancer of the blood. It does not usually
form solid tumors. Sarcomas arise in bone, muscle, fat, bloodvessels,
cartilage, or other soft or connective tissues of the body. They are relatively
uncommon. Melanomas are cancers that arise in the cells that make the pigment
in skin.
Cancer has been recognized for thousands of years as a human ailment,
yet only in the past century has medical science understood what cancer really
is and how it progresses. Cancer specialists, called oncologists, have made
remarkable advances in cancer diagnosis, prevention, and treatment. Today, more
people diagnosed with cancer are living longer. However, some forms of the
disease remain frustratingly difficult to treat. Modern treatment can
significantly improve quality of life and may extend survival.
Signs
and symptoms
When cancer begins, it produces no symptoms. Signs and symptoms
appear as the mass grows or ulcerates. The findings that result depend on the
cancer's type and location. Few symptoms are specific. Many frequently occur in
individuals who have other conditions. Cancer can be difficult to diagnose and
can be considered a "great imitator.
Local symptoms
Local symptoms may occur due to the mass of the tumor or its
ulceration. For example, mass effects from lung cancer can block 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 blockages in the bowel, affecting bowel habits. Masses in
breasts or testicles may produce observable lumps. Ulceration can cause
bleeding that can lead to symptoms such as coughing up blood (lung cancer),
anemia or rectal bleeding (colon cancer), blood in the urine (bladder cancer),
or abnormal vaginal bleeding (endometrial or cervical cancer). Although localized
pain may occur in advanced cancer, the initial tumor is usually painless. Some
cancers can cause a buildup of fluid within the chest or abdomen.
Systemic symptoms
Systemic symptoms may occur due to the body's response to the
cancer. This may include fatigue, unintentional weight loss, or skin changes.
Some cancers can cause a systemic inflammatory state that leads to ongoing
muscle loss and weakness, known as cachexia.
Some types of cancer such as Hodgkin disease, leukemias and
cancers of the liver or kidney can cause a persistent fever.
Some systemic symptoms of cancer are caused by hormones or other
molecules produced by the tumor, known as paraneoplastic syndromes. Common
paraneoplastic syndromes include hypercalcemia which can cause altered mental
state, constipation and dehydration, or hyponatremia that can also cause
altered mental status, vomiting, headache or seizures.
METASTASIS
Cancer can spread from its original site by local spread,
lymphatic spread to regional lymph nodes or by hematogenous spread via the
blood to distant sites, known as metastasis. When cancer spreads through the
blood, it may spread through the body but is more likely to travel to certain
areas depending on the cancer type. The symptoms of metastatic cancers depend
on the tumor location and can include enlarged lymph nodes (which can be felt
or sometimes seen under the skin and are typically hard), enlarged liver or
enlarged spleen, which can be felt in the abdomen, pain or fracture of affected
bones and neurological symptoms.
CAUSES
The majority of cancers, some 90–95% of cases, are due to genetic
mutations from environmental and lifestyle factors. The remaining 5–10% are due
to inherited genetics. Environmental refers to any cause that is not inherited
genetically, such as lifestyle, economic, and behavioral factors and not merely
pollution. Common environmental factors that contribute to cancer death include
tobacco (25–30%), diet and obesity (30–35%), infections (15–20%), radiation
(both ionizing and non-ionizing, up to 10%), lack of physical activity, and
pollution. Psychological stress does not appear to be a risk factor for the
onset of cancer, though it may worsen outcomes in those who already have cancer.
It is not generally possible to prove what caused a particular
cancer because the various causes do not have specific fingerprints. 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, the cancer
may have developed for one of those reasons. Excepting the rare transmissions
that occur with pregnancies and occasional organ donors, cancer is generally
not a transmissible disease.
CHEMICALS
Exposure to particular substances have been linked to specific
types of cancer. These substances are called carcinogens.
Tobacco smoke, for example, causes 90% of lung cancer. It also
causes cancer in the larynx, head, neck, stomach, bladder, kidney, esophagus
and pancreas. Tobacco smoke contains over fifty known carcinogens, including
nitrosamines and polycyclic aromatic hydrocarbons.
Tobacco is responsible for about one in five cancer deaths
worldwide and about one in three in the developed world. Lung cancer death
rates in the United States have mirrored smoking patterns, with increases in
smoking followed by dramatic increases in lung cancer death rates and, more recently,
decreases in smoking rates since the 1950s followed by decreases in lung cancer
death rates in men since 1990.
In Western Europe, 10% of cancers in males and 3% of cancers in
females are attributed to alcohol exposure, especially liver and digestive
tract cancers. Cancer from work-related substance exposures may cause between 2
and 20% of cases, causing at least 200,000 deaths. Cancers such as lung cancer
and mesothelioma can come from inhaling tobacco smoke or asbestos fibers, or
leukemia from exposure to benzene.
DIET AND EXERCISE
Diet, physical inactivity and obesity are related to up to 30–35%
of cancer deaths. In the United States, excess body weight is associated with
the development of many types of cancer and is a factor in 14–20% of cancer
deaths. A UK study including data on over 5 million people showed higher body
mass index to be related to at least 10 types of cancer and responsible for
around 12,000 cases each year in that country. Physical inactivity is believed
to contribute to cancer risk, not only through its effect on body weight but
also through negative effects on the immune system and endocrine system. More
than half of the effect from diet is due to overnutrition (eating too much),
rather than from eating too few vegetables or other healthful foods.
Some specific foods are linked to specific cancers. A high-salt
diet is linked to gastric cancer. Aflatoxin B1, a frequent food contaminant,
causes liver cancer. Betel nut chewing can cause oral cancer. National
differences in dietary practices may partly explain differences in cancer
incidence. For example, gastric cancer is more common in Japan due to its
high-salt diet while colon cancer is more common in the United States.
Immigrant cancer profiles mirror those of their new country, often within one
generation.
INFECTION
Worldwide approximately 18% of cancer deaths are related to
infectious diseases. This proportion ranges from a high of 25% in Africa to
less than 10% in the developed world. Viruses are the usual infectious agents
that cause cancer but cancer bacteria and parasites may also play a role.
Oncoviruses (viruses that can cause cancer) include human
papillomavirus (cervical cancer), Epstein–Barr virus (B-cell
lymphoproliferative disease and nasopharyngeal carcinoma), Kaposi's sarcoma
herpesvirus (Kaposi's sarcoma and primary effusion lymphomas), hepatitis B and
hepatitis C viruses (hepatocellular carcinoma) and human T-cell leukemia
virus-1 (T-cell leukemias). Bacterial infection may also increase the risk of
cancer, as seen in Helicobacter pylori-induced gastric carcinoma. Parasitic
infections associated with cancer include Schistosoma haematobium (squamous
cell carcinoma of the bladder) and the liver flukes, Opisthorchis viverrini and
Clonorchis sinensis (cholangiocarcinoma).
RADIATION
RADIATION
Radiation exposure such as ultraviolet
radiation and radioactive material is a risk factor for cancer. Many
non-melanoma skin cancers are due to ultraviolet radiation, mostly from
sunlight. Sources of ionizing radiation include medical imaging and radon gas.
Ionizing radiation is not a particularly
strong mutagen. Residential exposure to radon gas, for example, has similar
cancer risks as passive smoking. Radiation is a more potent source of cancer
when combined with other cancer-causing agents, such as radon plus tobacco
smoke. Radiation can cause cancer in most parts of the body, in all animals and
at any age. Children are twice as likely to develop radiation-induced leukemia
as adults; radiation exposure before birth has ten times the effect.
Medical use of ionizing radiation is a small
but growing source of radiation-induced cancers. Ionizing radiation may be used
to treat other cancers, but this may, in some cases, induce a second form of
cancer. It is also used in some kinds of medical imaging.
Prolonged exposure to ultraviolet radiation
from the sun can lead to melanoma and other skin malignancies. Clear evidence
establishes ultraviolet radiation, especially the non-ionizing medium wave UVB,
as the cause of most non-melanoma skin cancers, which are the most common forms
of cancer in the world.
Non-ionizing radio frequency radiation from
mobile phones, electric power transmission and other similar sources has been
described as a possible carcinogen by the World Health Organization's
International Agency for Research on Cancer. Evidence, however, has not
supported a concern. This includes that studies have not found a consistent
link between mobile phone radiation and cancer risk.
HEREDITY
The vast majority of cancers are
non-hereditary (sporadic). Hereditary cancers are primarily caused by an
inherited genetic defect. Less than 0.3% of the population are carriers of a
genetic mutation that has a large effect on cancer risk and these cause less
than 3–10% of cancer. Some of these syndromes include: certain inherited
mutations in the genes BRCA1 and BRCA2 with a more than 75% risk of breast
cancer and ovarian cancer, and hereditary nonpolyposis colorectal cancer (HNPCC
or Lynch syndrome), which is present in about 3% of people with colorectal
cancer, among others.
Statistically for cancers causing most
mortality, the relative risk of developing colorectal cancer when a
first-degree relative (parent, sibling or child) has been diagnosed with it is
about 2. The corresponding relative risk is 1.5 for lung cancer, and 1.9 for
prostate cancer. For breast cancer, the relative risk is 1.8 with a
first-degree relative having developed it at 50 years of age or older, and 3.3
when the relative developed it when being younger than 50 years of age.
Taller people have an increased risk of
cancer because they have more cells than shorter people. Since height is
genetically determined to a large extent, taller people have a heritable
increase of cancer risk.
PHYSICAL AGENTS
Some substances cause cancer primarily
through their physical, rather than chemical, effects. A prominent example of
this is prolonged exposure to asbestos, naturally occurring mineral fibers that
are a major cause of mesothelioma (cancer of the serous membrane) usually the
serous membrane surrounding the lungs. Other substances in this category, including
both naturally occurring and synthetic asbestos-like fibers, such as
wollastonite, attapulgite, glass wool and rock wool, are believed to have
similar effects. Non-fibrous particulate
materials that cause cancer include powdered metallic cobalt and nickel and
crystalline silica (quartz, cristobalite and tridymite). Usually, physical
carcinogens must get inside the body (such as through inhalation) and require
years of exposure to produce cancer.
Physical trauma resulting in cancer is
relatively rare. Claims that breaking
bones resulted in bone cancer, for example, have not been proven. Similarly,
physical trauma is not accepted as a cause for cervical cancer, breast cancer
or brain cancer. One accepted source is frequent, long-term application of hot
objects to the body. It is possible that repeated burns on the same part of the
body, such as those produced by kanger and kairo heaters (charcoal hand
warmers), may produce skin cancer, especially if carcinogenic chemicals are
also present. Frequent consumption of scalding hot tea may produce esophageal
cancer. Generally, it is believed that cancer arises, or a pre-existing cancer
is encouraged, during the process of healing, rather than directly by the
trauma. However, repeated injuries to the same tissues might promote excessive
cell proliferation, which could then increase the odds of a cancerous mutation.
Chronic inflammation has been hypothesized to
directly cause mutation. Inflammation can contribute to proliferation,
survival, angiogenesis and migration of cancer cells by influencing the tumor
microenvironment. Oncogenes build up an inflammatory pro-tumorigenic
microenvironment.
HORMONES
Some hormones play a role in the development
of cancer by promoting cell proliferation. Insulin-like growth factors and
their binding proteins play a key role in cancer cell proliferation,
differentiation and apoptosis, suggesting possible involvement in
carcinogenesis.
Hormones are important agents in sex-related
cancers, such as cancer of the breast, endometrium, prostate, ovary and testis
and also of thyroid cancer and bone cancer. For example, the daughters of women
who have breast cancer have significantly higher levels of estrogen and
progesterone than the daughters of women without breast cancer. These higher
hormone levels may explain their higher risk of breast cancer, even in the absence
of a breast-cancer gene. Similarly, men of African ancestry have significantly
higher levels of testosterone than men of European ancestry and have a
correspondingly higher level of prostate cancer. Men of Asian ancestry, with
the lowest levels of testosterone-activating androstanediol glucuronide, have
the lowest levels of prostate cancer.
Other factors are relevant: obese people have
higher levels of some hormones associated with cancer and a higher rate of
those cancers. Women who take hormone replacement therapy have a higher risk of
developing cancers associated with those hormones. On the other hand, people
who exercise far more than average have lower levels of these hormones and lower
risk of cancer. Osteosarcoma may be promoted by growth hormones. Some treatments and prevention approaches
leverage this cause by artificially reducing hormone levels and thus
discouraging hormone-sensitive cancers.
Autoimmune diseases
There is an association between celiac
disease and an increased risk of all cancers. People with untreated celiac
disease have a higher risk, but this risk decreases with time after diagnosis
and strict treatment, probably due to the adoption of a gluten-free diet, which
seems to have a protective role against development of malignancy in people
with celiac disease. However, the delay in diagnosis and initiation of a
gluten-free diet seems to increase the risk of malignancies.[79] Rates of
gastrointestinal cancers are increased in people with Crohn's disease and
ulcerative colitis, due to chronic inflammation. Also, immunomodulators and
biologic agents used to treat these diseases may promote developing
extra-intestinal malignancies.
DIAGNOSIS
Radiation exposure such as ultraviolet
radiation and radioactive material is a risk factor for cancer. Many
non-melanoma skin cancers are due to ultraviolet radiation, mostly from
sunlight. Sources of ionizing radiation include medical imaging and radon gas.
Ionizing radiation is not a particularly
strong mutagen. Residential exposure to radon gas, for example, has similar
cancer risks as passive smoking. Radiation is a more potent source of cancer
when combined with other cancer-causing agents, such as radon plus tobacco
smoke. Radiation can cause cancer in most parts of the body, in all animals and
at any age. Children are twice as likely to develop radiation-induced leukemia
as adults; radiation exposure before birth has ten times the effect.
Medical use of ionizing radiation is a small
but growing source of radiation-induced cancers. Ionizing radiation may be used
to treat other cancers, but this may, in some cases, induce a second form of
cancer. It is also used in some kinds of medical imaging.
Prolonged exposure to ultraviolet radiation
from the sun can lead to melanoma and other skin malignancies. Clear evidence
establishes ultraviolet radiation, especially the non-ionizing medium wave UVB,
as the cause of most non-melanoma skin cancers, which are the most common forms
of cancer in the world.
Non-ionizing radio frequency radiation from
mobile phones, electric power transmission and other similar sources has been
described as a possible carcinogen by the World Health Organization's
International Agency for Research on Cancer. Evidence, however, has not
supported a concern. This includes that studies have not found a consistent
link between mobile phone radiation and cancer risk.
Chemotherapy medications
Albumin-bound or
nab-paclitaxel - Abraxane
Adriamycin - doxorubicin
Carboplatin :
Paraplatin
Cyclophosphamide : Cytoxan
Daunorubicin :
Cerubidine, DaunoXome
Doxorubicin :
DOXIL
Epirubicin : Ellence
Fluorouracil also called 5-fluorouracil
or 5-FU -- Adrucil
Gemcitabine --Gemzar
Eribulin)
Ixabepilone)
Methotrexate
Mutamycin
Mitoxantrone :
Novantrone
Vinorelbine --Navelbine
Taclitaxel ----Taxol
Docetaxel -- Taxotere
Thiotepa
Vincristine
Capecitabine
