June 12, 2000
Volume 52, No. 35
Study identifies post-surgery kidney cancer risk
By Lillian Kim
Emory researchers have discovered that kidney cancer patients with high platelet counts are at least four times more likely to die following removal of the cancerous kidney than patients with normal platelet levels.
The study concludes that thrombocytosis, a condition in which platelet counts exceed 400,000 per milliliter, is a new and powerful indicator of prognosis for patients with renal cell carcinoma who undergo radical nephrectomy, a procedure in which the entire cancerous kidney is surgically removed. This is the first time this association has been noted, said John Petros, who headed the study.
"This has intrinsic value as a prognostic test," said Petros, associate professor of urology. "Any test that will give patients and doctors a more individualized picture of the patients' personal prognosis is very important."
The findings were presented last month at the American Urological Association's 95th annual neeting in Atlanta. In addition to Petros, other study researchers included Fray Marshall, chair of the urology department; Muta Issa, assistant professor and chief of urology at the VA Hospital; and Casey O'Keefe, a urology resident. Petros is director of urologic research at the School of Medicine and the VA.
The urologists reviewed the medical records of 173 consecutive patients with renal cell carcinoma, the most common form of kidney cancer, who underwent radical nephrectomy at Emory Hospital between 1993 and 1999. Of the 173 patients, 153 had normal platelet counts and 20 were defined as having thrombocytosis. The groups were similar in terms of cancer stage.
The cause-specific death rate for patients with normal platelet levels was 9.8 percent, and their average length of survival was 18.3 months. By comparison, the cause-specific death rate for patients with thrombocytosis was 45 percent, and their average length of survival was only 11.4 months.
An update on this study further strengthens the association between thrombocytosis and survival chances, showing a sixfold increase in the cancer-specific death rate for patients with renal cell carcinoma.
The researchers don't yet know how elevated platelet levels affect patient outcomes, but several plausible, well-formulated hypotheses exist. The simplest explanation is that platelets (tiny disk-shaped structures in blood chiefly known for their role in blood clotting) may coat cancer cells, making them less detectable to the immune system.
Another possibility involves interleukin-6 (IL-6), a type of protein that can affect the immune system response. Renal cell carcinoma produces IL-6, which can increase platelet counts. Some combination of these mechanisms may turn out to be the link between high platelet count and higher rates of death.
"You could have a tumor making IL-6," Petros said. "The IL-6 could be increasing the platelet count. The platelets could be making platelet-derived growth factor, which could be feeding the tumor."
According to the American Cancer Society, 31,200 new cases of kidney
cancer will be diagnosed this year. The organization also said renal cell
carcinoma accounts for about 85 percent of all kidney tumors and represents
2 percent of all adult cancers. Renal cell carcinoma primarily occurs in
adults between 50 and 70 years old, and men are twice as likely as women
to be diagnosed. Radical nephrectomy is the standard treatment.