Breast cancer screening is an ongoing experiment in which hundreds of thousands of women, perhaps thousands of radiologists and hundreds of pathologists have participated for about forty years. Its hypothesis is: early detection will improve outcomes. Screening is continually being evaluated because it’s difficult to assess whether outcomes have actually improved and, if they have, whether the improvements are due to early detection.
Screening does not prevent breast cancer. In fact mammography increases the risk of getting breast cancer. Plus, since there is no cure for breast cancer and it can always recur, screening does not save lives. I think the original hope was that early detection itself would be the cure. I think the hope persists. And, I think it’s one of the reasons why so many asymptomatic women decide to be screened year after year. Breast cancer screening is more complicated however, than one would hope.
First, not all breast cancers are life-threatening. There are some that are so slow-growing that women live out their lives never knowing they had breast cancer. Some types of ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS) will never progress at all. DCIS and LCIS are usually confined, either to a duct or a lobule, and are less than one centimeter in diameter when detected. They may or may not be life-threatening. However, since there is currently no way to tell which of the DCIS and LCIS cancers will grow and metastasize and no way to distinguish between very slow-growing and faster growing cancers, they’re all treated as if they were life-threatening.
For all intents and purposes, women with non-life-threatening breast cancers are well. Detecting their breast cancer and then treating it harms them. They will always be on the alert for signs of a recurrence that will never happen.
Second, radiologists’ skills range from eagle-eyed expertise to being so inaccurate one might as well toss a coin. I discovered toss-a-coin radiologists when I reviewed the research on computer-aided-detection and learned that their data had been eliminated from data analyses.
Although in practice radiologists’ decisions are more complicated, it’s sufficient to divide them into two alternatives: “yes, I see something suspicious” vs. “no, I don’t see something suspicious.” If we do that, there are four possible outcomes: “false positives,” “false negatives,” “true positives” or “true negatives.”
“True negatives” occur when radiologists don’t detect an abnormality and the women don’t have breast cancer. All is well. Of the four possible outcomes, only “true negatives” never cause harm.
“False negatives” happen when radiologists don’t detect an abnormality and the women have breast cancer. Radiologists miss abnormalities when they’re obscured by other tissues in the breast or can’t be distinguished from normal tissue. “False negatives” increase fear and stress in women who discover their breast cancer was missed and who believe early detection always makes a difference. Most people don’t know there are breast cancers that can be treated successfully no matter when they’re discovered.
“False positives” may occur when radiologists see something suspicious in a mammogram. Once a radiologist suspects something might be wrong, he or she may ask for additional diagnostic mammograms, callbacks in three to six months or ultrasound examinations. If the radiologist remains suspicious, biopsies are taken and tissue specimens sent to a pathologist for microscopic examination. Pathologists are the final judges. When they decide specimens do not contain malignant cells, radiologists’ decisions become “false positives.”
Although it’s always a relief to learn that one does not have breast cancer, “false positives” may be harmful. Almost all women are anxious during the waiting period between the screening mammogram and the pathologist’s report. Biopsies may be painful; they may be disfiguring. For some women the stress is extreme and never completely dissipates. They’re harmed.
Third, “true positives” occur when pathologists confirm radiologists’ suspicions. Well women are harmed when pathologists make mistakes.
I believe the public was made aware of pathologists’ errors first in 1977. In 1972, the National Cancer Institute (NCI) launched the Breast Cancer Detection Demonstration Project. Over 250,000 women were to be screened. In 1977, the NCI asked a pathologist to review the pathology of 506 breast lesions less than one centimeter in diameter. He found 66 mistakes---women who had been diagnosed with breast cancer, had had mastectomies, but didn’t have breast cancer. A great debate about the actual number ensued. The debate was never resolved. And, the 66 women were never informed of the possible misdiagnoses.
That was forty years ago, but apparently pathologists still make mistakes. In a July 19th 2010 New York Times article, Dr. Shahla Masood, the head of pathology at the University of the Florida College of Medicine (Jackson), described diagnosing DCIS as “a 30-year history of confusion and differences of opinion”…it “occasionally comes down to the flip of a coin.” The article also reported the experience of Dr. Lagios, a pathologist at St. Mary’s Medical Center in San Francisco who reviews slides for women seeking a second opinion. In 2007-2008 he reviewed 597 cases and found discrepancies in 141; DCIS was misdiagnosed in 27 of the cases.
It seems that as radiologists become more and more capable of detecting smaller and smaller breast cancers, the problems for pathologists and women whose breast cancers are being detected earlier and earlier are getting worse. If that’s so and continues to be true, we can expect that more and more well women will be harmed.
Next post: two more complications---computer-aided-detection and ionizing radiation.
