New Test Could End Pap Smear ‘Gray Area’
A new test for cancer of the cervix, used in conjunction with the standard Pap smear, could help warn women of early abnormalities and lead to earlier detection, a UC Irvine researcher reported Monday.
Eric Stanbridge, a professor in the College of Medicine, said the test could help reduce “false negatives,” in which a woman is told her Pap smear results were within normal limits, when in fact she has undetected traces of cancer or precancerous cells. He is awaiting approval to try the test with about 500 women nationwide.
Stanbridge, who holds a doctorate in medical microbiology, reported his findings at a science writers’ seminar held by the American Cancer Society in Newport Beach.
He and a fellow researcher, Dr. Shu-Yuan Lio, an associate clinical professor and pathologist at St. Joseph Hospital in Orange, found that the test appears to reliably detect malignancies and potentially cancerous lesions in what is now a “gray area” of Pap smear results.
Cervical cancer is the second-most common malignancy, after breast cancer, among women. The American Cancer Society predicts that 13,700 women nationwide will be diagnosed with cervical cancer this year and that 4,900 women will die of it.
Detection of the cancer improved dramatically in the 1940s with the development of the Pap smear, a sampling of cells from the uterus, generally performed annually. But the accuracy of the test is hampered by false negative results, Stanbridge said.
When cytologists study Pap smears, abnormal results generally fall into two categories: carcinoma or dysplasia, which are irregular cells prone to turning cancerous.
“But there are two gray areas” of abnormal cells that do not appear to be either carcinoma or dysplasia, he said. One is “atypical glandular cells of undetermined significance”; the other is “atypical squamous cells of undetermined significance.” Stanbridge and Lio studied the former category, which shows up in about 0.5%, or 250,000, of the 50 million Pap smears performed annually.
Stanbridge said the cells present a dilemma for doctors, because 60% of the cases turn out to be benign, but the rest are associated with “significant lesions.” So gynecologists have to decide whether to recommend that the patient undergo a biopsy, costing $400 to $1,200, or wait and have a repeat Pap smear, he said.
“You could argue, ‘Let’s wait six months.’ That might be all right, but it might not be all right,” he said. Doctors, fearful of being sued, might recommend biopsies for all cases, he said.
In Stanbridge’s tests, the Pap smear is treated with a dye that is picked up by an antigen in the cervical cancer cell.
Stanbridge and Lio looked at the past cases of 99 women whose Pap smears showed atypical glandular cells and who later had biopsies or other treatment to detect cancer. After dyeing the slides for the antigen, they looked up the women’s eventual diagnoses. In every case in which the antigen was present, the woman had been diagnosed with cancer or dysplasia, he said.
The antigen staining “is a very useful discriminator” when there has been a diagnosis of the atypical cells, Stanbridge said.
He and Lio are now awaiting approval from the National Cancer Institute to begin a study of 500 women with the abnormal cells at health centers nationwide during the next two or three years. The antigen test would be applied to their Pap smears and all the women would undergo biopsies for further diagnosis. The antigen test results then would be compared with the biopsy results to determine the test’s accuracy.
If the antigen test--at $50 each--is proven accurate, it will could mean a savings of $50 million to $70 million per year, assuming all women with the abnormal cells undergo biopsies, he said. “That’s 150,000 unnecessary biopsies,” he said.
