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 Nearly one in five suspected cases of skin cancer are likely
diagnosed as more advanced than they really are, researchers found.
Similarly, nearly one in five are likely diagnosed as less severe
when they're actually more severe.
"The diagnosis is made by a human," said lead author Dr. Joann
Elmore, of the University of Washington School of Medicine in
Seattle. "There is no molecular marker or machine that will tell us
what the diagnosis is."
Doctors who analyze and interpret biopsy samples are called
pathologists. Elmore said pathologists are not to blame for
inconsistent results, however. The cases tend to be difficult to
interpret.
"I had my own skin biopsy about a decade ago," she said. "I ended up
getting three different interpretations from three different
people."
"I realized this was an area I wanted to study and quantify," she
said.
Skin cancer is the most common form of cancer in the United States,
according to the Center for Disease Control and Prevention (CDC).
The deadliest form of skin cancer in known as melanoma.
More than 76,500 people in the U.S. were diagnosed with melanoma
skin cancer in 2014, according to the CDC. Nearly 9,500 people died
of it that year.
Skin cancer is diagnosed after doctors take a sample of
suspicious-looking skin from a patient. The sample is then sent to a
lab where a pathologist looks at thin slices of the skin under a
microscope to see if there are any signs of cancer. If cancer is
found, the pathologists assigns it a stage, ranging from 1 to 5,
with stage 5 being a cancer that has likely spread throughout the
body.
For the new study, the researchers used 240 skin samples broken into
sets of 36 or 48. The sets were then sent to 187 pathologists in 10
states for diagnoses. The same pathologists were asked to review the
same set of slides at least eight months later.
For the earliest melanoma, known as stage 1, about 77 percent of
pathologists issued the same diagnoses in both phases of the study.
Similarly, about 83 percent of pathologists issued the same
diagnoses twice for the most advanced melanoma cases.
Pathologists were less likely to confirm their diagnoses during the
study's second phase for melanomas in stage 2 through 4, according
to the results in The BMJ.
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The researchers also assembled a panel of three experienced
pathologists to review the cases. The proportion of diagnoses the
panel agreed with varied from 25 percent for stage 2 to 92 percent
for stage 1.
Overall, the researchers say, if real-world melanoma diagnoses were
reviewed by such an expert panel, only about 83 percent would be
confirmed.
They estimate that 8 percent of real-life cases are likely assigned
too high a stage. About 9 percent of cases are assigned too low a
stage.
"Thankfully most of the biopsies are not of invasive melanoma," said
Elmore.
Dr. Ashfaq Marghoob, a dermatologist with Memorial Sloan-Kettering
Cancer Center in New York City, said the results show that
pathologists have high certainty when diagnosing biopsies that fall
on the extremes of the stages.
"All the in-between cases, there is a potential you may waver," said
Marghoob, who wasn't involved with the new study.
"This subjectivity has long been understood and recognized by both
dermatologists and pathologists and has been demonstrated in
previous studies," said Dr. Jennifer DeFazio, who is also a
dermatologist at Memorial Sloan-Kettering and was also not involved
with the new study.
Marghoob said the pathologist may diagnose a skin sample differently
based on how they're feeling that day or any number of factors.
"For me, it’s a study to (remind doctors that) pathology is not an
exact science," said Marghoob.
SOURCE: http://bit.ly/2t5WzvK The BMJ, online June 28, 2017.
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