By Jonny Lupsha, Wondrium Staff Writer
There are several methods doctors use to screen patients for cancer. Some means of detecting cancer include mammograms, endoscopies, and colonoscopies. How effective is breast cancer screening?
The World Health Organization’s definition of “screening” for a disease essentially boils down to identifying an otherwise unrecognized disease through the use of a rapid test. When it comes to cancer screening, the four most common screenings are for cervical cancer, by a Pap smear; breast cancer, by a mammogram; colon cancer, by a colonoscopy; and prostate cancer, by a prostate-specific antigen (PSA) test.
Artificial intelligence (AI) software is being tested to detect breast cancer where doctors may have missed it. Doctors in Budapest have had success implementing the software for use in five hospitals, so far. Aside from AI, how effective is breast cancer screening? In his video series What Science Knows about Cancer, Dr. David Sadava, Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center in Duarte, CA, explains breast cancer screening.
How Is Cancer Screened?
“What are the detection methods for screening?” Dr. Sadava asked. “They include feeling—palpation, it’s called—looking for lumps of the breast or prostate. Secondly, of course, are internal methods: X-rays like a mammogram or an endoscope for looking at stomach cancer […] a colonoscopy for colon cancer. Third, of course, are biochemical and molecular markers.”
Biochemical and molecular markers look for a chemical that’s unique to the cancer cell. For example, if it can be detected in blood, like if cancer cells are leaking out into the blood, a biochemical or molecular marker would be a useful test.
“Screening tests are not perfect,” Dr. Sadava said. “How good is a test? There are two criteria for evaluating screening: reliability and validity. Reliability: that means reproducibility, the consistency with which a test gives the same result. Validity has two components: first, sensitivity and, second, specificity.”
But what is validity? Validity asks if a test actually distinguishes between people with cancer and people without it. In other words, does the test work? As Dr. Sadava said, the two components of validity are sensitivity and specificity. Sensitivity means the proportion of people who have the disease who test positive for it in a screening. Specificity means the proportion of people who don’t have the test and correctly test negative for it.
How Effective Is Breast Cancer Screening?
Three tests are typically done to screen for breast cancer, and they’re done every one to two years. Those tests are a breast self-exam, a clinical breast exam, and a mammogram.
“Breast self exam has a woman carefully examining her breast for lumps,” Dr. Sadava said. “The sensitivity is 21%, which means it misses 80% of breast cancers. The specificity is 30%, which means 70% of the time the woman feels a lump, it’s not breast cancer.”
Clinical breast exams are done by a physician or well-trained nurse. According to Dr. Sadava, their sensitivity rate is 60%, missing 40% of cancers. Unlike breast self exams, a clinical breast exam has much higher specificity. When doctors and nurses find a lump in a woman’s breast, the likelihood that it’s breast cancer is 95%. One in every 10 breast cancer diagnoses come from clinical exams.
“Much more widely used are mammograms,” he said. “Tens of millions of women get these every year. The sensitivity of mammograms ranges between 80 and 90%. Specificity: greater than 95%; very few false positives.”
What Science Knows about Cancer is now available to stream on Wondrium.