Researchers Pursue Promising Cervical Cancer Vaccine
But it won't replace the Pap test any time soon, experts say
SUNDAY, March 27, 2005 (HealthDay News) -- With news of a promising vaccine to protect against cervical cancer, it's possible the great work of the late Dr. George Nicholas Papanicolaou may fade in the not-too-distant future into an asterisk in the history of medicine.
Papanicolaou, a cytopathologist at New York Hospital-Cornell Medical Center, was the developer of the Pap test.
But first, news about the vaccine: In a trial of more than 1,100 women aged 15 to 25 in North America and Brazil, three injections of the vaccine during a six-month period reduced the infection rate by 95 percent. And the vaccine provided complete protection against precancerous growths associated with the two viral strains, according to a report in the Nov. 13 issue of The Lancet. Much more work needs to be done before this vaccine is ready for the public, so reliance on the Pap test is going to continue for a while.
Papanicolaou, who died in 1962, developed a simple, inexpensive test in the 1920s that became one of the few major victories in the history of the fight against cancer. It took until the mid-1950s before his test, nicknamed the Pap test, was finally fully appreciated by mainstream medicine. But once it was embraced, the mortality rate from cervical cancer in the United States began a free-fall.
Death from cervical cancer is 70 percent less than the days before women began having a periodic Pap test. This, in turn, transformed cancer of the cervix into a relatively rare malignancy in the United States. In the developing world, however, cervical cancer is still a significant malignancy, and it is there that an effective vaccine is expected to shine most brightly.
According to the American Cancer Society, 10,520 U.S. women were expected to develop cervical cancer in 2004, and the mortality was projected at 3,900 women. By contrast, 215,000 women were projected to develop breast cancer. Worldwide, 511,000 women develop cervical cancer each year, and about half die. It is the leading cancer killer among women in the developing world.
So popular is the Pap test in the United States that an estimated 10 million women continue to have it unnecessarily. These women have had a hysterectomy, rendering them incapable of developing the disease because they lack a cervix. No cervix, no cervical cancer.
Habits, it seems, die hard. And that's a good thing for women who still have a cervix, because there is no vaccine yet in general use and won't be for several years. What's more, the vaccines under clinical development now have limited protective value to women who are sexually active. For the most reliable protection, women may need to be vaccinated before exposure or infection through sexual contact to the human papillomaviruses (HPV).
It isn't clear how much post-infecton protection will be conferred to these HPVs. There are two strains in particular that trigger the persistent infection leading to cervical cancer. So, the vaccines may be of primary value to the next generation, for girls who will be teenagers when the vaccines are approved and administered.
In the meantime, as successful as the Pap test has been, it isn't perfect. A Pap test may miss precancerous cell changes or a pathologist may misdiagnose a smear as positive when it is really normal, or as negative when it isn't. Cancer authorities say that is why it is important to have frequent Pap tests. If one is a false negative, the next is likely to result in an accurate diagnosis. It usually takes several years for abnormal cytology to develop into cancer.
The American Cancer Society has recommended a standard Pap test annually, beginning three years after women begin having vaginal intercourse, but no later than when they are 21 years old. Screening should be done every year with the standard Pap test or every two years using the newer liquid-based Pap test.
Beginning at age 30, women who have no risk factors or who had three normal Pap test results in a row may get screened every two to three years with either the standard or liquid-based Pap test.
For more on cervical cancer, visit the National Cancer Institute.