The information in this post comes from an article in a recent New Yorker magazine written by Dr. Siddhartha Mukherjee, an oncologist and author of the Pulitzer Prize-winning book, The Emperor of All Maladies. It deals with efforts to find satisfactory methods to detect cancers.
Mammography is especially problematic because it “reveals
only the shadow of a tumor—it cannot divine the tumor’s nature.” That is, mammography
can’t tell whether the tumor is aggressive or has already spread or will remain
inert. Added to this ambiguity is the prevalence of false positives—test
results that indicate cancer where none exists. Only nine percent of people who
test positive actually have cancer. People with false positives are sent for biopsies,
“a risky, invasive process—which can involve a punctured lung, bleeding, or
other complications—with no benefit.” At the same time, aggressive cancers can
be missed because their detectable symptoms don’t appear at the time of a
screening. Patients with such cancers can even die between annual tests. The
apparent benefit of screening, Mukherjee says, is misleading because it disproportionately
detects tumors that are less likely to be lethal in the first place. In
contrast to the dubious benefits of mammography, colonoscopies pay off. Studies
have proven a fifty percent reduction in deaths from colorectal cancer among
those who received colonoscopies.
Now, scientists have found that cancer can be detected with
blood tests. Fragments of our DNA circulate in our bloodstreams. Using this
fact, researchers have found concrete evidence of tumor-derived DNA in cancer
patients’ blood. They’ve developed a multi-cancer early detection blood test—one
that can identify more than fifty types of cancer, including pancreatic and
ovarian. To determine the value of blood tests as a screening tool, they
conducted a major study in the UK, enrolling more than 15,000 participants. One
result of the study showed that only six of the 1,254 cancer-free participants
received false positives—a remarkably low rate. Unfortunately, the test’s
ability to identify Stage I cancers was meager—just above 16 percent. It did
better on more advanced cancers. But, of course, the whole point of screening
is early detection.
Cancer screening is clearly a work in progress. Mukherjee
hopes that “Perhaps, in time, we’ll build tools that can not only detect cancer’s
presence but predict its course…that may one day tell us not only where a
cancer began but whether it’s likely to pose a threat to health.” Stay tuned.
For an introduction to this blog, see I Just Say No; for a list of blog topics, click the Topics tab.
