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:
Anal cancer
Bladder cancer
Bone cancer
Breast cancer
Cervical cancer
Colon cancer
Colorectal cancer
Endometrial cancer
Kidney cancer
Leukemia
Liver cancer
Lymphoma
Ovarian cancer
Pancreatic cancer
Prostate cancer
Stomach cancer
Testicular cancer
Thyroid cancer
Vaginal cancer
Vulvar cancer
Latest cancer research
We are a leading publisher of worldwide
cancer news and research. You can find all our latest news in our cancer news
section.
The rest of this article will focus on
what cancer is, what causes cancer, the symptoms, diagnosis and available
treatments.
Fast facts on cancer
Here are some key points about cancer.
More detail and supporting information is in the main article.
More than 575,000 people die of cancer,
and more than 1.5 million people are diagnosed with cancer per year in the US.
Cancer is considered to be one of the
leading causes of morbidity and mortality worldwide.
The financial costs of cancer in the US
per year are an estimated $263.8 billion in medical costs and lost
productivity.
African Americans are more likely to die
of cancer than people of any other race or ethnicity.
It is believed that cancer risk can be
reduced by avoiding tobacco, limiting alcohol intake, limiting UV ray exposure
from the sun and tanning beds and maintaining a healthy diet, level of fitness
and seeking regular medical care.
Screening can locate cervical cancer,
colorectal cancer and breast cancer at an early, treatable stage.
Vaccines such as the human
papillomavirus (HPV) vaccine assists in preventing some cervical, vaginal,
vulvar, and oral cancers. A vaccine for hepatitis B can reduce liver cancer
risk.
According to the World Health
Organization (WHO), the numbers of new cancer cases is expected to rise by
about 70% over the next 20 years.
The most common sites of cancer among
men are lung, prostate, colon, rectum, stomach and liver.
The most common sites of cancer among
women are breast, colon, rectum, lung, cervix and stomach.
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.
Cancer
classification
There
are five broad groups that are used to classify cancer.
Carcinomas
are characterized by cells that cover internal and external parts of the body
such as lung, breast, and colon cancer.
Sarcomas
are characterized by cells that are located in bone, cartilage, fat, connective
tissue, muscle, and other supportive tissues.
Lymphomas
are cancers that begin in the lymph nodes and immune system tissues.
Leukemias
are cancers that begin in the bone marrow and often accumulate in the
bloodstream.
Adenomas
are cancers that arise in the thyroid, the pituitary gland, the adrenal gland,
and other glandular tissues.
Cancers
are often referred to by terms that contain a prefix related to the cell type
in which the cancer originated and a suffix such as -sarcoma, -carcinoma, or
just -oma. Common prefixes include:
Adeno-
= gland
Chondro-
= cartilage
Erythro-
= red blood cell
Hemangio-
= blood vessels
Hepato-
= liver
Lipo- =
fat
Lympho-
= white blood cell
Melano-
= pigment cell
Myelo-
= bone marrow
Myo- =
muscle
Osteo-
= bone
Uro- =
bladder
Retino-
= eye
Neuro-
= brain
Cancer
diagnosis and stagingDoctor looking at x-ray
Early
detection of cancer can greatly improve the odds of successful treatment and
survival. Physicians use information from symptoms and several other procedures
to diagnose cancer.
Imaging
techniques such as X-rays, CT scans, MRI scans, PET scans, and ultrasound scans
are used regularly in order to detect where a tumor is located and what organs
may be affected by it. Doctors may also conduct an endoscopy, which is a
procedure that uses a thin tube with a camera and light at one end, to look for
abnormalities inside the body.
Extracting
cancer cells and looking at them under a microscope is the only absolute way to
diagnose cancer. This procedure is called a biopsy. Other types of molecular
diagnostic tests are frequently employed as well. Physicians will analyze your
body's sugars, fats, proteins, and DNA at the molecular level. For example,
cancerous prostate cells release a higher level of a chemical called PSA
(prostate-specific antigen) into the bloodstream that can be detected by a
blood test. Molecular diagnostics, biopsies, and imaging techniques are all
used together to diagnose cancer.
After a
diagnosis is made, doctors find out how far the cancer has spread and determine
the stage of the cancer. The stage determines which choices will be available
for treatment and informs prognoses. The most common cancer staging method is
called the TNM system. T (1-4) indicates the size and direct extent of the
primary tumor, N (0-3) indicates the degree to which the cancer has spread to
nearby lymph nodes, and M (0-1) indicates whether the cancer has metastasized
to other organs in the body. A small tumor that has not spread to lymph nodes
or distant organs may be staged as (T1, N0, M0), for example.
TNM
descriptions then lead to a simpler categorization of stages, from 0 to 4, where
lower numbers indicate that the cancer has spread less. While most Stage 1
tumors are curable, most Stage 4 tumors are inoperable or untreatable.
Recent
developments on cancer diagnosis
Blood
test could replace biopsy for cancer diagnosis
A
simple blood test could be on the way to replacing the biopsy as the gold
standard for detecting cancer, saving lives and money, according to researchers
in the UK. In their study, carried out on known or suspected primary or
secondary lung cancer who were about to undergo surgery, the blood test was
accurate in predicting the presence of cancer cells in nearly 70% of cases.
Symptoms
of cancer
Cancer
symptoms are quite varied and depend on where the cancer is located, where it
has spread, and how big the tumor is. Some cancers can be felt or seen through
the skin - a lump on the breast or testicle can be an indicator of cancer in
those locations. Skin cancer (melanoma) is often noted by a change in a wart or
mole on the skin. Some oral cancers present white patches inside the mouth or
white spots on the tongue.
Other
cancers have symptoms that are less physically apparent. Some brain tumors tend
to present symptoms early in the disease as they affect important cognitive
functions. Pancreas cancers are usually too small to cause symptoms until they
cause pain by pushing against nearby nerves or interfere with liver function to
cause a yellowing of the skin and eyes called jaundice. Symptoms also can be
created as a tumor grows and pushes against organs and blood vessels. For
example, colon cancers lead to symptoms such as constipation, diarrhea, and
changes in stool size. Bladder or prostate cancers cause changes in bladder
function such as more frequent urination or infrequent urination.
Lymph
nodes
Swollen
or enlarged lymph nodes can be a symptom, although lymph nodes can also become
swollen when fighting infection (cold or flu).
As
cancer cells use the body's energy and interfere with normal hormone function,
it is possible to present symptoms such as fever, fatigue, excessive sweating,
anemia, and unexplained weight loss. However, these symptoms are common in
several other maladies as well. For example, coughing and hoarseness can point
to lung or throat cancer as well as several other conditions.
When
cancer spreads, or metastasizes, additional symptoms can present themselves in
the newly affected area. Swollen or enlarged lymph nodes are common and likely
to be present when the cancer starts to spread.
If
cancer spreads to the brain, patients may experience vertigo, headaches, or
seizures. Spreading to the lungs may cause coughing and shortness of breath. In
addition, the liver may become enlarged and cause jaundice and bones can become
painful, brittle, and break easily. Symptoms of metastasis ultimately depend on
the location to which the cancer has spread.
Treatments
for cancer
Cancer
treatment depends on the type of cancer, the stage of the cancer (how much it
has spread), age, health status, and additional personal characteristics. There
is no single treatment for cancer, and patients often receive a combination of
therapies and palliative care. Treatments usually fall into one of the
following categories: surgery, radiation, chemotherapy, immunotherapy, hormone
therapy, or gene therapy.
1)
Surgery
Surgery
is the oldest known treatment for cancer. If a cancer has not metastasized, it
is possible to completely cure a patient by surgically removing the cancer from
the body. This is often seen in the removal of the prostate or a breast or
testicle. After the disease has spread, however, it is nearly impossible to
remove all of the cancer cells. Surgery may also be instrumental in helping to
control symptoms such as bowel obstruction or spinal cord compression.
Innovations
continue to be developed to aid the surgical process, such as the iKnife that
"sniffs" out cancer. Currently, when a tumor is removed surgeons also
take out a “margin” of healthy tissue to make sure no malignant cells are left
behind. This usually means keeping the patients under general anesthetic for an
extra 30 minutes while tissue samples are tested in the lab for “clear
margins”. If there are no clear margins, the surgeon has to go back in and
remove more tissue (if possible). Scientists from Imperial College London say
the iKnife may remove the need for sending samples to the lab.
In a
study carried out at Washington University School of Medicine in 2014,
researchers found a way of visualizing cancer cells using high-tech glasses
designed to make it easier for surgeons to distinguish between cancerous and
healthy tissue. Viewed through the glasses, cancer cells appear to glow blue
under a special light, thanks to a fluorescent marker injected in the tumor
that attaches only to cancerous and not to healthy cells. Also, the lighter the
shade of blue, the more concentrated the cancer cells are.
Promising
results of an early small trial at Duke University Medical Center in Durham, NC
have suggested a new injectable agent that makes cancer cells in a tumor
fluoresce, could help surgeons remove all of the cancerous tissue on the first
attempt. Tests continue to be carried out.
2)
RadiationRadiotherapy treatment on a man
Radiation
treatment, also known as radiotherapy, destroys cancer by focusing high-energy
rays on the cancer cells. This causes damage to the molecules that make up the
cancer cells and leads them to commit suicide.
Radiotherapy
utilizes high-energy gamma-rays that are emitted from metals such as radium or
high-energy x-rays that are created in a special machine. Early radiation
treatments caused severe side-effects because the energy beams would damage
normal, healthy tissue, but technologies have improved so that beams can be
more accurately targeted. Radiotherapy is used as a standalone treatment to
shrink a tumor or destroy cancer cells (including those associated with leukemia
and lymphoma), and it is also used in combination with other cancer treatments.
3)
Chemotherapy
Chemotherapy
utilizes chemicals that interfere with the cell division process - damaging
proteins or DNA - so that cancer cells will commit suicide. These treatments
target any rapidly dividing cells (not necessarily just cancer cells), but
normal cells usually can recover from any chemical-induced damage while cancer
cells cannot. Chemotherapy is generally used to treat cancer that has spread or
metastasized because the medicines travel throughout the entire body. It is a
necessary treatment for some forms of leukemia and lymphoma. Chemotherapy
treatment occurs in cycles so the body has time to heal between doses. However,
there are still common side effects such as hair loss, nausea, fatigue, and
vomiting. Combination therapies often include multiple types of chemotherapy or
chemotherapy combined with other treatment options.
4)
Immunotherapy
Immunotherapy
aims to get the body's immune system to fight the tumor. Local immunotherapy
injects a treatment into an affected area, for example, to cause inflammation
that causes a tumor to shrink. Systemic immunotherapy treats the whole body by
administering an agent such as the protein interferon alpha that can shrink
tumors. Immunotherapy can also be considered non-specific if it improves
cancer-fighting abilities by stimulating the entire immune system, and it can
be considered targeted if the treatment specifically tells the immune system to
destroy cancer cells. These therapies are relatively young, but researchers
have had success with treatments that introduce antibodies to the body that
inhibit the growth of breast cancer cells. Bone marrow transplantation
(hematopoetic stem cell transplantation) can also be considered immunotherapy
because the donor's immune cells will often attack the tumor or cancer cells
that are present in the host.
5)
Hormone therapy
Several
cancers have been linked to some types of hormones, most notably breast and
prostate cancer. Hormone therapy is designed to alter hormone production in the
body so that cancer cells stop growing or are killed completely. Breast cancer
hormone therapies often focus on reducing estrogen levels (a common drug for
this is tamoxifen) and prostate cancer hormone therapies often focus on
reducing testosterone levels. In addition, some leukemia and lymphoma cases can
be treated with the hormone cortisone.
6) Gene
therapy
The
goal of gene therapy is to replace damaged genes with ones that work to address
a root cause of cancer: damage to DNA. For example, researchers are trying to
replace the damaged gene that signals cells to stop dividing (the p53 gene)
with a copy of a working gene. Other gene-based therapies focus on further
damaging cancer cell DNA to the point where the cell commits suicide. Gene
therapy is a very young field and has not yet resulted in any successful
treatments.
Using
cancer-specific immune system cells to treat cancer
Scientists
from the RIKEN Research Centre for Allergy and Immunology in Yokohama, Japan,
explained in the journal Cell Stem Cell (January 2013 issue) how they managed
to make cancer-specific immune system cells from iPSCs (induced pluripotent
stem cells) to destroy cancer cells.
The
authors added that their study has shown that it is possible to clone versions
of the patients’ own cells to enhance their immune system so that cancer cells
could be destroyed naturally.
Hiroshi
Kawamoto and team created cancer-specific killer T-lymphocytes from iPSCs. They
started off with mature T-lymphocytes which were specific for a type of skin
cancer and reprogrammed them into iPSCs with the help of “Yamanaka factors”.
The iPSCs eventually turned into fully active, cancer-specific T-lymphocytes -
in other words, cells that target and destroy cancer cells.
Cancer
preventionQuit smoking written on calendar
Quitting
smoking can significantly decrease your risk of getting cancer.
Cancers
that are closely linked to certain behaviors are the easiest to prevent. For
example, choosing not to smoke tobacco or drink alcohol significantly lower the
risk of several types of cancer - most notably lung, throat, mouth, and liver
cancer. Even if you are a current tobacco user, quitting can still greatly
reduce your chances of getting cancer.
Skin
cancer can be prevented by staying in the shade, protecting yourself with a hat
and shirt when in the sun, and using sunscreen. Diet is also an important part
of cancer prevention since what we eat has been linked to the disease.
Physicians recommend diets that are low in fat and rich in fresh fruits and
vegetables and whole grains.
Certain
vaccinations have been associated with the prevention of some cancers. For
example, many women receive a vaccination for the human papillomavirus because
of the virus's relationship with cervical cancer. Hepatitis B vaccines prevent
the hepatitis B virus, which can cause liver cancer.
Some
cancer prevention is based on systematic screening in order to detect small
irregularities or tumors as early as possible even if there are no clear
symptoms present. Breast self-examination, mammograms, testicular
self-examination, and Pap smears are common screening methods for various
cancers.
Researchers
from Northwestern University Feinberg School of Medicine in Chicago reported in
the journal Circulation that the 7 steps recommended for protection against
heart disease can also reduce the risk of developing cancer,. They include
being physically active, eating a healthy diet, controlling cholesterol,
managing blood pressure, reducing blood sugar and not smoking.
Targeting
cancers for new drug therapies
Researchers
at The Institute of Cancer Research reported in the journal Nature Reviews Drug
Discovery (January 2013 issue) that they have found a new way of rapidly
prioritizing the best druggable targets online. They managed to identify 46
previously overlooked targets.
The
researchers used the canSAR database together with a tool and were able to
compare up to 500 drug targets in a matter of minutes. With this method, it is
possible to analyze huge volumes of data to discover new drug targets, which
can lead to the development of effective cancer medications.
The
scientists analyzed 479 cancer genes to determine which ones were potential
targets for medications. Their approach was effective - they found 46 new
potentially “druggable” cancer proteins.
Not
only will this approach lead to much more targeted cancer drugs, but also
considerably cheaper ones, the authors added.
