New research published in the journal Cancer suggests that current cervical cancer screening guidelines underestimate incidence rates of the disease in the US, as well as the risk of older women developing cervical cancer.
Under current guidelines set by the American Cancer Society, women between the ages of 21 and 29 should be screened for cervical cancer every 3 years, while women aged between 30 and 65 should be screened every 5 years.
However, recommendations state that women over the age of 65 who have had regular cervical cancer screening with normal results should not continue to be screened.
But according to the research team, led by Anne Rositch, PhD, of the University of Maryland School of Medicine, women over the age of 65 are at highest risk of the disease – something that is not reflected in current US cervical cancer incidence rates.
The problem with past estimates of cervical cancer rates in the US, the researchers say, is that women who have undergone a hysterectomy – removal of the uterus – are still included in calculations, even though the procedure has eliminated their risk of cervical cancer.
“In order to make accurate estimates of the true rates of cervical cancer by age in the US and monitor trends in the occurrence of disease, it is important to calculate the occurrence of cervical cancer only among women who are at risk,” explains Rositch.
Therefore, the team set out to gain a truer reflection of the prevalence of cervical cancer among American women. They did this by assessing cervical cancer incidence and hysterectomy prevalence between 2000 and 2009.
Cervical cancer risk ‘highest for women aged between 65 and 69’
The researchers found that when they eliminated women who had a hysterectomy, cervical cancer rates were much higher than past estimates, particularly among older women.
Before accounting for hysterectomies, overall cervical cancer incidence rates stood at 11.7 cases per 100,000 women. When taking hysterectomies out of the equation, incidence rates stood at 18.6 per 100,000.
The researchers note that past research has indicated that cervical cancer incidence rates are highest between the ages of 40 and 44, at 15.6 per 100,000, before leveling off.
However, once the investigators had eliminated women who had hysterectomies, they found that overall incidence rates increased with age, peaking at 24.7 cases per 100,000 for women aged between 65 and 69 years. This was even more pronounced among black women of this age group, at 53.0 cases per 100,000
The team also found higher incidence among black women of all age groups than previously reported. Before correcting for hysterectomies, figures suggested that black women had a 62% higher rate of cervical cancer than white women. But after eliminating hysterectomies, the team found black women actually had an 89% higher rate than white women.
Current screening guidelines ‘should be reviewed’
Based on these findings, the researchers note that existing national cervical cancer screening guidelines should be reviewed.
“Current guidelines recommend exiting women with recent negative screening from routine screening at age 65 years, and yet our corrected calculations show that women just past this age have the highest rate of cervical cancer,” says senior study author Patti Gravitt, PhD, of the Johns Hopkins Bloomberg School of Public Health in Baltimore, MD, adding:
“It will be important to clarify in future studies whether the continued increase in cancer rates with age and the higher rates in black women represent a failure in our screening programs or a failure of the women to be screened, so that appropriate interventions can be developed to reduce the burden of cancer in these women.”
The researchers conclude that although many cases of cervical cancer have been prevented as a result of early detection and treatment, their findings highlight that the disease remains a major problem. Therefore, they stress the need for a broader uptake of the human papillomavirus vaccine for prevention of cervical cancer in the US.
Cervical cancer used to be the leading cause of cancer death for women in the United States. However, in the past 40 years, the number of cases of cervical cancer and the number of deaths from cervical cancer have decreased significantly. This decline largely is the result of many women getting regular Pap tests, which can find cervical precancer before it turns into cancer. In certain populations and geographic areas of the United States, cervical cancer incidence and death rates are still high, due in large part to limited access to cervical cancer screening.
According to the Centers for Disease Control and Prevention, nearly 12,000 women were diagnosed with cervical cancer in 2010 (the most recent year numbers are available), and over 3,900 women died from the disease. Worldwide, cervical cancer is the third most common cancer among women and the second most frequent cause of cancer-related death, accounting for nearly 300,000 deaths annually. In developing nations, it is often the most common cause of cancer-related death among women and a leading cause of death overall.
Virtually all cases of cervical cancer are caused by specific types of human papillomavirus (HPV). There are more than 100 types of HPV, of which more than 40 can be sexually transmitted. Among these, about 15 are considered to be cancer-causing, or high-risk, types. Two of these high-risk types, HPV-16 and HPV-18, cause about 70% of cervical cancers worldwide. HPV infection is very common, but it usually goes away on its own. Persistent HPV infections, however, can cause cellular abnormalities that sometimes develop into cervical cancer if not treated.
The Food and Drug Administration (FDA) has approved two vaccines to prevent HPV infection: Gardasil® and Cervarix®. Both vaccines are highly effective in preventing infections with HPV types 16 and 18. Gardasil also prevents infection with HPV types 6 and 11, which cause 90 percent of genital warts.
The HPV vaccines work like other immunizations that guard against viral infections. The investigators hypothesized that the unique surface components of HPV might create an antibody response that is capable of protecting the body against infection, and that these components could be used to form the basis of a vaccine.
The HPV surface components can interact with one another to form virus-like particles (VLP) that are not infectious, because they lack DNA. However, these VLPs can attach to cells and stimulate the immune system to produce antibodies that can prevent the complete papillomavirus, in future encounters, from infecting cells.
Although HPV vaccines can help prevent future HPV infection, they do not help eliminate existing HPV infections.
Gardasil and Cervarix are highly effective in preventing infection with the types of HPV they target. The vaccines have been shown to provide protection against persistent cervical HPV 16/18 infections for up to 8 years, which is the maximum time of research follow-up thus far. More will be known about the total duration of protection as research continues.
HPV vaccination has also been found to prevent nearly 100 percent of the precancerous cervical cell changes that would have been caused by HPV 16/18.
Widespread vaccination has the potential to reduce cervical cancer deaths around the world by as much as two-thirds, if all women were to get the vaccine. With the new findings on the prevalence of cervical cancer in the US, the importance of prevention strategies — including the HPV vaccine, condom use, and regular screenings — will become even greater.
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