Cancer is a group of many related diseases. All forms of cancer cause cells in
the body to change and grow in an abnormal way. Normal body cells divide and
grow in an orderly fashion. But cells changed by cancer can divide and grow out
of control. This out-of-control-growth damages normal body tissues and disrupts
the ability of organs to function, as they should. During the early years of a
person’s life, normal cells divide rapidly until adult size is reached. After
that, normal cells of most tissues divide only to replace worn-out tissue and to
repair injuries. Cancer cells, however, continue to grow. Often the cells form
tumors (lumps) that compress, invade, and destroy normal tissue. Unless the
cancer is treated, the tumors can grow and spread. If cells break away from such
a tumor, they can travel through the bloodstream or the lymph system to other
areas of the body. There, they may settle and form “colony” tumors. In
their new location, the cancerous cells begin growing again. The spread of a
tumor to a new site is called metastasis. Leukemia, a form of cancer, does not
usually form a tumor. Instead, cancer cells invade the blood and blood-forming
organs (spleen, lymphatic system, and bone marrow). It is important to realize
that not all tumors are cancerous. Benign tumors, which stay in one place and
have limited growth, is usually not life threatening. Cancer is classified by
the part of the body in which it develops, by its appearance under the
microscope, and by the results of a laboratory test. Since cancer is not a
single disease, each type of cancer behaves differently. What’s more, different
cancers also respond in various ways to different types of treatment. That’s why
people with cancer need treatment that is aimed at their specific forms of the
disease. In America, half of all men and on third of all women will develop
cancer during their lifetime. Cancer is not necessarily fatal, however. Today,
millions of people are living with cancer or have been cured. And the risk of
developing many types of cancer can be reduced by changes in a person’s
lifestyle. The sooner a cancer is found, and the sooner treatment begins, the
better a patient’s chances are of a cure. What is Liver Cancer? The liver is the
largest internal organ of the body. It weighs about 3 pounds and accounts for
about 2% of a person’s body weight. It is sheltered by the lower right ribs and
it is found underneath the right lung, separated from it by a muscle known as
the diaphragm. It is shaped like a pyramid and divided into right and left
lobes. Each of these lobes is further divided into segments. The liver, unlike
most other organs, receives blood form two sources. The hepatic artery supplies
the liver with blood that is rich in oxygen. The portal vein carries
nutrient-rich blood from the intestines to the liver. Because the liver is
involved in many important metabolic functions, a person cannot survive without
a liver. Some nutrients and vitamins absorbed by the intestines are stored in
the liver until other organs need them. Other nutrients must be metabolized
(chemically changed) in the liver before they can be used by the body for energy
or to build and repair tissues. Carbohydrate, protein, and lipid metabolism all
depend on proper liver function. Blood levels of glucose and controlled by the
liver. Glucose is a type of sugar that serves as the main source of energy for
most tissues and organs in the body. The lover produces albumin. Albumin is a
blood protein with several essential functions that include keeping a proper
balance of fluid between tissues and the bloodstream, and transporting many
hormones and drugs through the bloodstream. Several clotting factors are made in
the liver. Without these factors to plug up damaged blood vessels, even small
cuts or scrapes would cause life-threatening bleeding. Without amino acid
metabolism by the liver, other tissues of the body could not produce the
structural proteins of our bones and connective tissues or enzymes (proteins
that regulate nearly all chemical processes of the body). The lover also plays a
part on the metabolism of lipids (fats) and makes cholesterol, which is an
essential part of the membranes that surround all cells and divide the cells
into organelles (specific parts of cells). The liver also inactivates many drugs
and toxic chemicals. If the liver is not working well, these substances can
build up and interfere with many of the body’s functions. The liver also
produces bile, which is needed for the intestines to absorb certain nutrients.
Types of Liver Tumors There are several types of malignant (cancerous) and
benign (non-cancerous) tumors that con form in the liver. Because these tumors
have different causes, are treated differently, and have a different prognosis
(outlook for survival), it is important to briefly review their names. Several
different types of cells form the liver. Different tumors can start in any of
these cell types. The most common type of benign liver tumor starts in blood
vessels. It is called a hemangoima. Most hemangiomas of the liver cause no
symptoms. Some may cause blood loss. This type of tumor can be cured by surgical
removal. Hepaticadenomas are benign tumors that start from hepatocytes (the main
type of liver cell). Most cause no symptoms but some cause abdominal (stomach
area) pain, an increased by long-term use of oral contraceptives (birth control
pills). This type of tumor can be cured by surgical removal. Hepaticadenomas are
benign tumors that start from hepatocytes (the main type of liver cell). Most
cause no symptoms but some cause abdominal (stomach area) pain, a mass in the
abdomen, or blood loss. The risk of having a hepatic adenoma is increased by
ling-term use of oral contraceptives ( birth control pills). This type of tumor
can be cured by surgical removal. Focal nodular hyperplasia (FNH) is a
tumor-like growth of several cell types (hepatocytes, bile duct cells, and
connective tissues.). FNH is also cured by surgical removal. Both FNH and
hepatic adenomas are more common in women that in men. There are four main types
of malignant liver tumors: Angiosarcomas or hemangiosarcomas begin from blood
vessels of the liver. The risk of developing an angiosarcoma is greatly
increased by exposure to vinyl chloride or to thorium dioxide (Thorotrast).
Vinyl chloride is a chemical used in manufacturing some kinds of plastics. In
the past, Thorotrast was a chemical injected into some patients as part of a
certain x-ray test. Once the cancer-causing properties of these chemicals were
recognized, steps were taken to eliminate or reduce the risk. Workers exposed to
vinyl chloride are strictly regulated, and plastics manufacturing processes have
been changed to lower exposure. Medical use of Thorotrast was stopped about 50
years ago. Angiosarcomas of the liver are rare, accounting for about 1% of liver
cancers. Unfortunately, they grow rapidly and are usually too widespread to be
removed surgically by the time they are found. Chemotherapy and radiation
therapy does not help much. The typical patient survives less than 6 months
after diagnosis. Cholangiocarcinoma is a type of adenocarcinoma (malignant
glandular tumor) that starts in small bile ducts within the liver. About 13% of
primary liver cancers are cholangiosarcomas. People with gallstones are
gallbladder inflammation, chronic ulcerative colitis (a longstanding
inflammation of the large bowel), or chronic infection with Clonorchis sinensis
(a parasitic worm found in parts of Asia) has an increased risk of developing
this cancer. Signs and symptoms may include abdominal pain, liver enlargement,
or jaundice (green-yellow coloration of the skin and eyes). Joundice without
abdominal pain is most typical of cholangiocarcinomas that start near the hilum
to the liver (the area where bile ducts exit the liver on their way to the
gallbladder). Cholangiocarcinomas in that area also known as Klatskin tumors.
Most cholangiocarcinomas cannot be completely removed by surgery, due to their
size and location within the liver. Chemotherapy and radiation therapy is also
not effective. For these reasons, their prognosis is poor, with an average
survival after diagnosis of about 6 months. When possible, complete surgical
removal is attempted. Surgery to bypass bile ducts blocked by cancer can
temporarily relieve some symptoms. Hepatoblastoma is a rare type of liver cancer
that is usually found in children less that 4 years old. Under the microscope,
the cells of hepatoblastoma resemble embryonic or fetal liver cells. About 70%
of children with this disease are treated successfully and the survival rate is
over 90% for early stage hepatoblastomas. In contrast with most adult liver
cancers, hepatoblastomas usually respond well to chemotherapy. Hepatocellular
carcinoma (also known as hepatoma or HCC) develops from hepatocytes (the main
type of liver cell). It is the most common type of primary liver cancer (cancer
beginning within the liver). HCC accounts for about 84% of primary liver
cancers. For this reason, the remaining sections of this document refer only to
HCC. There are several subtypes of HCC which appear slightly different when
viewed under a microscope. The fibrolamellar subtype of HCC is the most
significant of these. Patients with fibrolamellar HCC are usually younger than
those with other subtypes. They are usually women and do not have diseases of
their non-cancerous liver tissue. Most importantly this subtype is associated
with a much better prognosis that other forms of HCC. In contrast to primary
liver cancers that form in the liver, metastatic or secondary liver tumors are
those that develop in other organs (such as the pancreas, colon, stomach,
breast, lung, etc.) and secondary metastasize (spread) to the liver. In the
United States and Europe, secondary liver tumors are more common than primary
liver cancer. The opposite is true for many areas of Asia and Africa. Do We Know
What Causes Liver Cancer? Although several risk factors for HCC are known, the
exact way in which these factors cause normal liver cells to become cancerous is
only partially understood. Scientists believe that cancers develop in two steps:
The first step requires damage to the DNA cells. DNA contains the instructions
for nearly every chemical process in our bodies. Some of these instructions help
cells to grow at a proper rate. If these instructions are altered, the cells may
grow too much and form a tumor. Fortunately, our cells have the ability to
repair our DNA, so that most DNA damage does not cause a cancer. The second step
in cancer formation requires cells to grow and divide. When cells divide shortly
after their DNA is damaged, two new “daughter cells” may be formed
before the original cell has time to repair its DNA damage. Both daughter cells
will have the same DNA error. Once this happens, it is too late to repair the
damage, which may eventually cause a cancer. Certain chemicals that cause liver
cancer, such as aflatoxins, are known to damage liver cells’ DNA. Recent studies
have shown that aflatoxins can damage the p53 gene. The DNA of these genes
normally works to prevent cells from growing too much. Damage to the p53 DNA can
lead to increased growth of cells and formation of cancers. Infection of liver
cells with hepatitis viruses can also cause DNA damage. These viruses have their
own DNA, which carries instructions on how to infect cells and produce more
viruses. In some patients this viral DNA can become inserted into the liver
cell’s DNA. An insertion of virus DNA can cause confusion in the DNA
instructions of a liver cell. If the virus interrupts instruction related to
cell growth control, a cancer may be formed. Cells of certain tissues such as
blood, skin, and the intestinal lining constantly wear out and must be replaced.
Under normal conditions, adult liver cells rarely wear out and rarely divide.
Only a small fraction of liver cells undergo cell division in response to minor
cell loss due to natural aging. However, if hepatitis viral infection, alcohol
abuse, or iron accumulation damages the liver, cells can die. This leads the
remaining liver cells to grow and divide. This growth and division can pass
damaged liver cell DNA (due to virus insertion, aflatoxin, or other causes) on
to the new “daughter” liver cells before it can be repaired. The
result is that cell instructions for growth control can be permanently altered,
and a cancer may form. Although scientists are making progress in understanding
this process, there are still some points that are not completely understood. It
is hoped that a more complete understanding will help in developing ways to
better prevent and treat liver cancers.
