It is common knowledge that women who suffer from cervical cancer have also shown thin, flat shaped papillomas in the vagina and outer cervix. Contrary to any of the many varieties of genital warts caused by the Human Papilloma Virus (HPV), the few cancer-associated forms of papillomas are almost invisible. Thanks to regular annual Pap tests it is possible to detect an HPV lesion likely to cause cervical cancer. This knowledge comes from case-control studies of the most common sexually transmitted disease. Although crucial to the detection and cure of cervical cancer, these case-control studies do not provide information on the dynamics of cumulative or persistent exposure to HPV infection.
From a public health point of view, it would be useful to know whether or not repeated incidences of HPV infections correlate with subsequent cervical cancer incidence since the ability to predict such an occurrence will help decision makers in the allotment of resources. Now, according to the results of a longitudinal epidemiological study led by Professor Eduardo L. Franco, Director of the McGill Division of Cancer Epidemiology, published in the December 26 edition of the Journal of the American Medical Association (JAMA) it seems there is indeed such a correlation to be made between these two incidences.
From 1993 to 2000, Professor Franco and his team of epidemiologists and oncologists from McGill University, Sâo Paulos Ludwig Institute for Cancer Research and the Bronxs Albert Einstein College of Medicine, investigated the natural history of HPV infection and squamous intraepithelial lesions (SIL), among a total of 1791 women, aged between 18 and 60, who were permanent residents of Sâo Paulo, Brazil, a high risk area for cervical cancer. These women were not currently pregnant and had no intention of becoming pregnant during the next 12 months, had an intact uterus and no current referrals for hysterectomy, had not had treatment for cervical disease in the previous 6 months and were ready to comply with all scheduled returns at least for the subsequent 2 years.
The incidence rate of squamous intraepithelial lesions (SIL) was of 0.72 % among women with no HPV infection at the two initial visits and of 8.68% among women with persistent infections for types 16 or 18 of HPV. Furthermore, women with persistent infections with any known oncogenic HPV types had 10.2 times greater risk of incident SIL than those who were free of HPV infection at their initial two visits.
In their article entitled "Persistent Human Papillomavirus Infection as a Predictor of Cervical Intraepithelial Neoplasia" Dr Franco and his colleagues explain how the results of their study "show a strong relationship between persistent HPV infection and SIL incidence particularly for HPV types 16/18." The integral version of this article is available on the JAMA website.
The study was supported by grants from the Ludwig Institute for Cancer Research, the U.S. National Cancer Institute and the Canadian Institutes of Health Research.
N.B. Professor Franco is chair of the XVIth World Congress of Epidemiology to be held in Montreal, at the Palais des Congrès, August 18 - 22, 2002.