By Stephen Ornes
Finding Solutions for Screening
Cancer screening faces roadblocks, even for cancers that have effective tests
By Stephen Ornes
What does the ideal cancer screening test look like? It’s conclusive, noninvasive, and costs about five bucks. It finds precancerous cells and can reveal whether a patient is genetically predisposed to developing the disease. It’s available to everyone, regardless of health insurance status, nationality or income.
And it’s a long way off. But that’s not for lack of trying: Since the 1950s, when the first simple screening for precursors to cervical cancer led to a drop in the U.S. incidence rate, funding for and research of screening tests have increased dramatically. With the mapping of the human genome and rapid strides in genetic research, scientists have been increasingly concentrating on biological or genetic markers that can flag a person’s propensity for cancer. Screening tests of the future could be simple blood or urine tests that preclude the need for uncomfortable procedures or surgery.
There won’t be one universal screening test. To borrow from Tolstoy, each malignancy is malignant in its own way. Some cancers, like colorectal and cervical cancer, can be found at early or precancerous stages via tried-and-true tests. Screening tools for others, like ovarian and pancreatic cancer, which are rarely detected at an early stage, have eluded researchers, despite considerable funding and study. A close look at the science of screening tests for these four cancers can reveal what has already been accomplished in the search for useful early warning signs—and what remains to be done.
CERVICAL CANCER: Herd immunity on the horizon
The history of cervical cancer shows that a simple screening test can make a big difference. In the 1940s, cancer of the cervix was a leading cause of death among young women. The 1950s saw the development of the Pap smear, a simple screening test that quickly reveals the presence of abnormal, possibly precancerous cells in the cervix. As the test became commonplace, rates of cervical cancer plummeted. Between 1955 and 1992, the incidence of cervical cancer dropped by nearly 75 percent.
More recently, scientists found that most cases of cervical cancer were due to infection by various types of the sexually transmitted human papillomavirus (HPV). In 2006, the U.S. Food and Drug Administration (FDA) approved the first HPV vaccine, which can provide protection against the two types of HPV that cause the majority of cervical cancers. A second vaccine is currently being studied in clinical trials.
It’s too soon to tell what impact the vaccine will have on cervical cancer, says epidemiologist Electra D. Paskett, who runs the Ohio State University’s Center for Population Health and Population Health Disparities, in Columbus. But if enough people get the vaccine, she says, the U.S. population could reach a state of “herd immunity,” in which the majority has protection through vaccination.
Despite the great successes of cervical cancer research, the disease remains a serious threat, especially to people who do not have access to screening tests. Globally, cervical cancer claims about 300,000 lives a year, and is the third largest cause of cancer death.
In the United States, Paskett says, underserved populations still have higher rates of cervical cancer than the general population. “Is it because they don’t get screened at the same rate or don’t get appropriate follow-up? I would say it’s a combination of both.”