FRIDAY, June 11, 2004 (HealthDayNews) -- All cancers are said to be "genetic" in origin. That is, they stem from mutations in DNA that cause cells to grow unchecked. But that's different from saying they're inherited, or passed from parent to child.
Cancer experts believe that between 5 percent and 10 percent of cancers are the results of single genes that have gone awry and that get transmitted across generations. These "susceptibility genes" put a person at substantially greater risk of developing cancer in specific organs.
The trigger for the tumor might simply be the passage of time, but it might also be a constellation of contact with things in the environment, such as cigarette smoke, certain chemicals, or other exposures.
Among the most well-known inherited tumors are those that affect the breasts and ovaries linked to mutations in two genes, BRCA1 and BRCA2. These gene flaws raise the lifetime risk of breast cancer to between 56 percent and 87 percent, compared to 11 percent in the general population. They increase the risk of ovarian cancer to between 16 percent and 44 percent from about 2 percent.
BRCA1 and its sibling mutation have also been associated with inherited forms of colorectal cancer and with prostate cancer in men. Inheritance is implicated in a rare form of colon tumor called hereditary nonpolyposis colorectal cancer, or HNPCC. And researchers have identified susceptibility genes for thyroid cancer and skin cancer.
A recent study by researchers in Germany and Sweden found that children whose parents had cancer were much more likely than their peers to develop the same illness.
The family connection was particularly strong for certain tumors. Men had a 15 percent chance of getting prostate cancer, anyone with a parent who'd had intestinal cancer had a 10 percent risk of the same ailment, and women had an 8.5 percent risk of breast cancer if their mother had it.
Sons of fathers with testicular cancer had four times the risk of developing the disease compared to sons from fathers without it. Brothers of affected men had a ninefold higher risk than normal of developing it, too.
But cancer experts stress that inheriting a susceptibility gene isn't the same as inheriting cancer. "If we have a mutation, it poses a greater risk or liability [of illness] but not a certainty," says Carolyn Farrell, director of the clinical genetics service at the Roswell Park Cancer Institute in Buffalo, N.Y.
Genetic counselors advise people with a strong family history of cancer to be especially vigilant about screening for the disease, such as breast mammography or colon imaging.
In the case of breast cancer, they may also encourage women to consider taking the drug tamoxifen to prevent tumors, and even discuss the possibility of removing the breasts and ovaries with women whose family history of these diseases is particularly lethal.
What about the remaining 90 percent of cancers -- what causes them? The vast majority -- perhaps 70 percent -- are thought to occur sporadically, Farrell says. That leaves about 20 to 25 percent which likely arise from an interaction between genes, the environment, and other factors that are not yet well understood.
The National Cancer Institute has more information about genetics and cancer.