Doctors Learn More about Diagnosing Rare Form of Cancer

Their experience treating a rare type of abdominal cancer has helped physicians at Wake Forest University Baptist Medical Center make a new discovery that may change the way it is diagnosed. The results are reported in the May issue of the American Journal of Surgical Pathology.

"Our study suggests that tumors of the appendix that have spread through the abdominal cavity all qualify as cancer," said Robert F. Bradley, M.D., principal investigator. "Previously, some of the tumors were classified as 'benign,' which we believe gives a false sense of how the tumor will behave."

Bradley, a pathology resident, and colleagues focused on 101 patients with pseudomyxoma peritonei, a rare form of cancer of the lining of the abdominal cavity. The cancer, which produces mucin, a "jelly-like" substance, usually originates in the appendix or colon and spreads to the abdominal lining. Bradley evaluated all available microscopic slides in cases proven to come from the appendix.

Wake Forest is one of a few centers in the country that offer a combined treatment - surgery to remove the tumor and then infusion of heated chemotherapy drugs into the abdominal cavity. Because it treats patients from all over the country with the disease, Wake Forest had a unique opportunity to clear up confusion about its diagnosis.

"Because it is so rare - less than 0.1 percent of appendices are removed for cancer - the disease has been plagued with controversy and confusing terminology," said Bradley.

Currently, many pathologists who study sections of the tumor after surgery classify it into three general categories: high-grade cancer, low-grade cancer, and benign. All of the patients normally receive the same treatment - the grade of the tumor indicates how patients will respond.

The investigators from Wake Forest compared the diagnoses made using these three grades with patients' outcome after receiving standardized treatment. Patients in the study, which is the largest to date of pseudomyxoma peritonei that originated from the appendix, were treated from 1993 to 2005.

The researchers found one-year, three-year and five-year survival rates were not significantly different for patients in the "low-grade cancer" and "benign" categories. However, patients in the "high-grade" category had significantly worse survival.

"Hopefully this will help resolve the confusion in diagnosis," said Bradley. "Our study shows that there is no separate 'benign' variant of the disease. Instead, physicians should expect those tumors that look 'benign' microscopically to behave like low-grade cancer. We now combine those cases into one diagnosis of low-grade carcinoma, for which the prognosis should be equally favorable with adequate treatment."

Bradley said the way the disease is diagnosed has implications for how it is viewed and treated.

"We hope this will lead to a more standardized diagnosis so that these patients' doctors understand exactly what it means," he said.