By David N. Leff
Like streets, libraries and airports, diseases are often named after celebrities associated with them. Lou Gehrig's disease, we know, spells amyotrophic lateral sclerosis. Woody Guthrie, the famous folk singer, died of Huntington's chorea. Betty Ford's mastectomy in the 1970s persuaded many breast cancer victims to come out of that horrendous closet.
Few people recognize Henrietta Lacks' disease — cancer of the uterine cervix. Yet, in death, that woman is known to virologists and cell biologists all over the scientific world by her extended acronym, HeLa.
Lacks, an African-American mother of five, died of cervical cancer in 1951 at the Johns Hopkins University hospital, in Baltimore. Yet in a sense she never died. Eight months before succumbing to her adenocarcinoma, Lacks donated a tumor biopsy section that became the first immortalized human cell line in biological history to survive in vitro.
Besides contributing to polio vaccine research, and helping set up virology and molecular biology generally, those immortal HeLa cells, with poetic justice, bid fare to save any number of women from the cervical cancer that killed Henrietta Lacks.
In the 1940s, cytologist George Papanicolau demonstrated that epithelial cells sloughing off from the surface of the uterine cervix, and properly stained, could show under the microscope whether or not that tissue was on its way to becoming malignant.
"Since its introduction," said oncological cell biologist Eric Stanbridge, of the University of California at Irvine, "the Pap smear test has led to a 70 percent decline in the mortality rate from invasive cervical cancer in the U.S. However, it remains the eighth leading cause of gynecological cancer." He cited estimates that "approximately 5,000 American women died of cervical cancer in 1997, and the majority of them did not have a Pap smear test in the previous five years."
"Despite this success," Stanbridge pointed out, "false negative results still occur in Pap tests, due to human errors in the labs, or cell sampling mistakes."
Stanbridge spoke Monday to science writers covering the 1998 meeting of the American Cancer Society, in Newport Beach, Calif.
"Testing Pap smears of cervical cells for an antigen called MN/CA9," he told BioWorld Today, "can tip scientists off to precancerous cervical lesions and malignant growths that may go undiscovered with current diagnostic techniques."
That antigen was jointly discovered in 1992 by a Czech and a Slovak molecular virologist, shortly before Czechoslovakia underwent political mitosis in 1993 to become the separate Czech and Slovak Republics. They found MN/CA9 in the cervical cancer HeLa cell line, four decades after its initial propagation, and made the antibody to it.
Jan Zavada, the Czech scientist, and his Slovak collaborator, Sylva Pastorekova, contacted Stanbridge because he had pioneered suppression of tumor cells by somatic cell hybridization. He used HeLa cells in this research. Stanbridge and his Czech and Slovak colleagues picked up the antigenic ball and ran with it.
Although promiscuous in almost all cervical cancers, MN/CA9 is not expressed at all in the normal cervix, which is a hollow cone protruding from the vaginal wall. It provides entry into and exit from the uterus.
Studies Target More Accurate Diagnoses
"Virtually 100 percent of cervical carcinomas, whether squamous [flat, scaly cells], adenosquamous or adenocarcinomatous," Stanbridge observed, "are positive for the expression of MN/CA9, which is a tumor-associated antigen."
He recalled: "We were interested, of course, in the utility of that antigen's expression with respect to diagnosis, for that one goes initially to Pap smears. In Pap test diagnosis," he continued, "there are two serious gray areas for the clinician — the so-called AGUS and ASCUS.
"AGUS," he explained, "stands for atypical glandular cells of undetermined significance.
"The problem for the clinician," Stanbridge went on, "is that AGUS diagnosis is not a diagnosis. There's certainly something abnormal about those cells, but the cytologist reviewing the Pap smear is not willing to make a call on that. His problem is that only a certain percentage of those smears will indeed correlate with a significant lesion at biopsy. So the oncologist is left with a dilemma of what to do about his or her patient."
Screening surveys show that about 40 percent of patients with a Pap smear diagnosis of AGUS will harbor precancerous or cancerous lesions; 60 percent will not.
"Some 250,000 of the 50 million Pap tests conducted each year in the U.S. are given a diagnosis of AGUS," Stanbridge noted, "but doctors can't determine if patients have significant lesions without costly invasive biopsies.
"We've examined this now," he recounted, "with the expression of the MN/CA9 antigen, and we show a very, very strong correlation between its staining in the AGUS smears, and a significant cancerous lesion." He added: "In those cases where the MN/CA9 is not expressed, there is none. So it appears to be a very good discriminator."
Preclinical Tests Pan Out
The AGUS study, he pointed out, "was retrospective and non-blinded."
"In that study," Stanbridge recounted, "we had the tissue biopsies — covering the entire spectrum from normal to malignant — and corresponding Pap smears. We looked at 99 archived samples selected for AGUS diagnosis by Pap test, for which we had tissue biopsies.
"Pathologists," he continued, "then stained those AGUS smears with antibody to the MN/CA9 antigen, to see if they were positive or negative for antigenic expression. Their results clearly showed that MN-negative AGUS Pap smears correlated with normal biopsies, whereas positives correlated with significant cancerous lesions.
"Thus," Stanbridge pointed out, "there were no false negatives with the antigen expression."
The second variant in the Pap smear gray area is ASCUS — atypical squamous cells of undetermined significance. Stanbridge and his team have not yet sought to correlate ASCUS with the MN/CA9 antigen, "but we think," he concluded, "that the antigenic technique appears promising for those cells as well."
He plans to begin multicenter clinical trials of this new MN/CA9 test as a useful biomarker in diagnosing AGUS, and to begin similar upcoming studies for ASCUS patients in the coming months. These are now awaiting final approval by the National Cancer Institute. *