Colon cancer is one of the most common types of cancer. Most
colon cancers are sporadic: that is, they are not inherited and cannot be
passed to your children. Although the cause is usually unknown, sporadic cancers
may occur due to environmental exposures. In other cases, mistakes (mutations)
can occur in genes by chance when a cell divides. Since these mutations occur
only in the cancer cells, they cannot be passed on to one’s children.
Sometimes, several members of a family will develop colon
cancer. In these cases, cancer is occurring more often than would be expected by
chance, yet does not appear to be clearly hereditary (passed from parent
to child). Very little is known about the causes of cancer in these families. It
is possible that interactions are occurring between genes and the environment or
among several genes. This type of moderately increased cancer risk can be called
a "familial colon cancer."
About 5-10% of colon cancers are believed to be hereditary. When
a person is at risk for hereditary cancer, this means that he or she has
inherited a gene with a change in it, called a mutation, that makes the person
more prone to developing cancer. Individuals who inherit a mutation in a cancer
susceptibility gene have a much greater chance of developing cancer. However,
not everyone with a cancer susceptibility gene mutation will develop cancer.
This article will focus on the most common inherited colorectal
cancer syndromes: hereditary nonpolyposis colorectal cancer (HNPCC), familial
adenomatous polyposis (FAP), and MYH-associated polyposis (MAP). Other
syndromes include juvenile polyposis syndrome (JPS), Peutz-Jeghers syndrome (PJS),
and the PTEN-hamartoma tumor syndrome. Genetic testing is available for all of
these syndromes. Genetic testing is usually done on a blood sample. The sample
is sent to a laboratory for analysis of one or more genes associated with a
syndrome and the results are reported back to your healthcare provider for
interpretation.
Hereditary nonpolyposis colorectal cancer (HNPCC)
HNPCC, also known as Lynch syndrome, is the most common form of
hereditary colon cancer, accounting for about 3 percent of all colorectal cancer
diagnoses each year. Although not everyone with HNPCC will develop colorectal
cancer, the risk is greatly increased compared with that of the general
population. For someone with HNPCC, the risk of developing colorectal cancer is
approximately 80 percent over his or her lifetime. Women with HNPCC also have a
60 percent lifetime risk of developing uterine cancer and up to a 12 percent
risk of developing ovarian cancer. Stomach cancer is the third most common type
of cancer associated with HNPCC; the lifetime risk is as high as 13 percent.
People with HNPCC also have a higher risk of developing other cancers in organs
such as the small intestine, pancreas, renal pelvis, and biliary tract.