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Wilms' tumor a lesser known foe to children

The word "cancer" is used to refer to a group of more than 100 diseases. Because of that, it can be hard to keep track of all the different types of cancers, and some are inevitably bound to gain more attention or headlines than others.

One type of cancer that does not garner many headlines is Wilms' tumor, the most common form of kidney cancer in children. Roughly 500 new cases of Wilms' tumor are diagnosed in the U.S. each year, while the Canadian Cancer Society reports that, between 2003 and 2007, 220 new cases of Wilms' tumor were diagnosed in children and youth ages 0-19. (Editor's Note: Wilms' tumor is extremely rare in adults.)

Despite its status as the most common form of kidney cancer in children, Wilms' tumor has no known cause. The CCS notes that 90 percent of Wilms' tumor cases develop sporadically and have no identifiable risk factors. While researchers have yet to link a specific cause to Wilms' tumor, they have extensively studied the formation of the kidneys in a baby and feel that, when something goes wrong during that formation, Wilms' tumor can result. An example of something going wrong during kidney formation is cells not maturing during the process. These cells instead stay like fetal cells, which can cluster and still be there after the baby is born. While these fetal cells often mature by the time a child becomes a toddler, sometimes they never mature and begin to grow out of control, resulting in a Wilms' tumor.

The symptoms of Wilms' tumor can mimic other conditions, meaning the presence of any of the following symptoms does not necessarily mean a child has kidney cancer. Instead, should any of these symptoms appear, parents should take their child to a physician immediately.

* painless lump in the abdomen

* fever

* blood in the urine

* diarrhea

* swelling of the abdomen

* pain in the abdomen

* high blood pressure

* changes to digestion, including loss of appetite, upset stomach, nausea and vomiting

* the appearance of large or distended veins across the abdomen

Because the cause of Wilms' tumor remains a mystery, the risk factors are difficult to pinpoint. But many of the known risk factors are hereditary. A child may inherit an abnormal gene from a parent, increasing the child's risk of Wilms' tumor, but not necessarily guaranteeing the tumor will develop. In fact, the American Cancer Society notes that only a small number of children with Wilms' tumor have a relative with the same cancer. The ACS also notes that Wilms' tumor is slightly more common among girls and African Americans, though the reasons for that are unknown.

Wilms' tumor has also been linked to children with certain birth defects. Roughly 10 percent of children with Wilms' tumor have a birth defect, most of which occur in syndromes, or groups of symptoms or problems that are commonly linked to certain changes in genes. In certain syndromes, part or even all of a gene might be missing, and these missing or abnormal genes can cause Wilms' tumor. Among the birth defects linked to Wilms' tumor are:

* Aniridia: This is a rare condition in which the iris of the eye, which gives the eye its color and controls the amount of light entering the eye, does not form completely.

* Hemihypertrophy: An overgrowth syndrome, hemihypertrophy occurs when one side of the body grows larger than the other.

* Hypospadias: This occurs in males when the urinary opening is not at the tip of the penis but on the underside instead.

* Undescended testicles: A condition that occurs when one or both testicles do not descend into the scrotum.

Treatment is successful for many children with Wilms' tumor, but the survival rate, as is the case with all cancers, varies depending on the stage of the tumor.

Wilm's tumor gets its name from Dr. Max Wilms, who wrote one of the first medical articles on the disease. More information on Wilms' tumor is available at www.cancer.org and www.cancer.ca.