Cervical cancer is the third most common cancer in women worldwide, but most American women can prevent it by being screened with tests that detect human papillomaviruses (HPV).
A new study led by University of New Mexico Comprehensive Cancer Center scientists shows that screening every three years instead of annually prevents most cervical cancers. And of the cancers that are found during routine screenings, most are caught before they've had a chance to spread, making them far easier to treat.
The results of the study were published ahead of the print version, in the December online edition of the International Journal of Cancer. UNM Regents' Professor Cosette Wheeler, PhD, led the study and says, "Cancer screening works and the vast majority of women who get cervical cancer simply don't get screened at all, or instead wait too long between screens."
Wheeler and her team worked with the New Mexico Tumor Registry to link their information with that of the New Mexico HPV Pap Registry. The state's Tumor Registry records all cases of cancer and all deaths due to cancer in the state. The HPV Pap Registry records all cervical cancer screening results, which include Pap and HPV tests, and all procedures to diagnose and treat cervical precancers - abnormalities that have not yet turned cancerous.
Combining data from the two statewide public health information systems provided a unique ability to understand the screening histories of women who developed cervical cancer throughout New Mexico. "This capacity is not available elsewhere," Wheeler says. "It serves as a model information system for cancer prevention in the United States."
Previous studies, Wheeler says, have used data from a single health care system, and often from the same insurer. The New Mexico data, however, include all information from the entire state, regardless of the women's insurance provider, insurance coverage, health care provider and location.
Wheeler's team included national and international experts and postdoctoral, graduate and undergraduate students who study health care delivery to improve cancer prevention across New Mexico. In this study, the screening records of each woman who was diagnosed with cervical cancer were compared with those of a control group of five New Mexican women without cervical cancer. The diagnosed women and the women in the control groups were matched on age, race, ethnicity and rural or urban geographic area.
Wheeler's team found that 61% of women in the control groups had been screened within the previous three years, but only 38% of the women with cervical cancer had been screened in the same period prior to their cancer diagnosis.
The researchers also compared the medical histories of women diagnosed with cervical cancer. Those who had been screened in the three years prior to diagnosis were half as likely to be diagnosed with localized cervical cancer as those who hadn't been screened. They were also 83% less likely to be diagnosed with cervical cancer that had spread.
"Screening is super important for catching cancers before they have spread," Wheeler says.
The team also showed that women who receive a negative screening test were very unlikely to be diagnosed with cervical cancer in the following three-and-a-half to five years. Many HPV infections will resolve naturally, Wheeler says, but the immune system needs time to act. She and her team found that more frequent screening offered no additional benefit.
"The value of a negative screen is huge," Wheeler says. "If you screen, we can show that screening prevents more than 80% of distant cancer and about 50% of local cancer. And the local cancer is easily treatable."
This study, she says, gives real-world evidence to assure New Mexican women and their health care providers that screening for cervical cancer every three years safely finds cancer early and that screening more frequently has no additional benefit.
In the end, the biggest problem Wheeler sees is that the United States has no organized way to remind women when the time comes for their three-year screening. "We need to fix this [lack of a central reminder system]," Wheeler says. "New Mexico can take the lead."
"Impact of screening on cervical cancer incidence: A population-based case-control study in the United States" was published in the December 13, 2019, online edition of International Journal of Cancer. The authors are: Rebecca Landy, Peter D. Sasieni, Christopher Mathews, Charles L. Wiggins, Michael Robertson, Yolanda J. McDonald, Daniel W. Goldberg, Isabel C. Scarinci, Jack Cuzick, Cosette M. Wheeler and the New Mexico HPV Pap Registry Steering Committee.
Cosette M. Wheeler, PhD, is a Regents' Professor in the Department of Pathology and the Department of Obstetrics & Gynecology at the UNM School of Medicine. She is a Senior Staff Investigator for Population Sciences and holds the Victor and Ruby Hansen Surface Endowed Chair in Translational Medicine and Public Health Sciences at the UNM Comprehensive Cancer Center. She also served as Director of the NCI NM HOPES-Cervical PROSPR Research Center and as Director of the NIAID EPIC-STI Center (Epidemiology and Prevention Interdisciplinary Center for Sexually Transmitted Infections).