By Jonny Lupsha, News Writer

Cancer deaths between 2016 and 2017 saw their sharpest decline yet, according to NPR. Researchers credit declining smoking rates and new treatments for the lower number of deaths. If more people got cancer screenings, the death rate would drop even more.

NPR reported Wednesday that cancer death rates have been on the decline for three decades at “about 1.5% a year.” However, one recent annual drop was at a rate of 2.2%, which NPR stated as the largest decline on record. This drop could be even larger if more people chose to get cancer screenings.

“Many smokers and former smokers are not following the advice to get screened with a low-dose CT scan to catch cancer early,” the article said. “In fact, a recent study found that only 4.4% of people eligible for this screening test actually got screened in 2015,” despite the test being free of charge under the Affordable Care Act.

Understanding Cancer Screenings

“The World Health Organization defines screening for disease, and here we’re talking about cancer, as the identification of unrecognized disease by the application of a rapid test,” said Dr. David Sadava, Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center.

Dr. Sadava said that the four most common kinds of cancer and their screenings are cervical cancer, which is tested by a Pap smear; breast cancer, via mammogram; colon cancer, tested via colonoscopy; and prostate cancer, by a PSA test. And while a screening isn’t perfect, nor is it a diagnosis, it’s a good indicator for disease or impending disease.

“A screening test sorts out apparently well people who probably don’t have a disease that they can’t tell they have from those who probably do have the disease,” Dr. Sadava said. “A screen when you detect something that’s probably cancer has to be followed up by biopsies and chemical tests of those types of cells, etc.”

Detection Methods and Effectiveness of Screening

There are several ways to detect cancer early on, including but not limited to the four most common methods listed above.

“They include feeling—’palpitation,’ it’s called—looking for lumps of the breast or prostate,” Dr. Sadava said. “A physician or trained person can look for lumps or swelling. Secondly, of course, are internal methods: X-rays like a mammogram or an endoscope for looking at the stomach cancer, and for a gut for endoscopy, a colonoscopy for colon cancer.”

“Third, of course, are biochemical and molecular markers. So we can look for a marker—a chemical that’s unique to a cancer cell, hopefully. And if we can detect it even in blood—a blood test where cancer cells are leaking it out into the blood—that would be very useful.”

How useful? Dr. Sadava mentioned that there are two criteria for determining the quality of a cancer screening. The first is reliability and the second is validity.

Reliability falls under the ability of the test to give reproducible, consistent results by multiple physicians at different times. Getting two independent and consistent results is often a good indicator of the screening test’s accuracy.

However, just to be safe, there’s the question of validity. “Validity has two components: first, sensitivity, and second, specificity,” Dr. Sadava said. “Sensitivity [is] the the proportion of people with the disease who test positive.”

“For example, for Pap smear, sensitivity is 95%, which means 19 out of 20 cancer cases are detected. However, we got a false negative there. One out of 20 women walk out of a Pap smear, the doctor looks at it and says it’s normal, but unfortunately the cancer goes on to develop. The Pap smear test is a very good test, but it has a 1-in-20 error rate.”

The second component of validity of a cancer screening is specificity. Dr. Sadava said that specificity refers to “the proportion of unaffected people who don’t have the cancer, who test negative.” This should be a much, much larger group, but occasionally someone will have a false positive, meaning they test positive for the disease despite not having it. False positives are costly and time-consuming for both the patient and his or her attending health care professionals, but fortunately false positives are rare.

Getting screened for precancerous cells may on occasion come with a false positive or false negative, but if all eligible people got tested, the rate of cancer deaths would sink even lower than it has in recent decades.

Dr. David Sadava contributed to this article. Dr. Sadava is Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center. Professor Sadava graduated from Carleton University as the science medalist with a B.S. with first-class honors in biology and chemistry. A Woodrow Wilson Fellow, he earned a Ph.D. in biology from the University of California, San Diego.