Missed Breast Lesions Found After the Fact
Nov. 30, 1999 (Chicago) -- Radiologists often say that it is difficult to
find very small lesions in dense breasts --which the breasts of younger women
often are -- with mammograms, but a study from Stanford University radiologists
suggests that about half of the "missed" cancers are found in
non-dense, or fatty, breasts.
Robyn L. Birdwell, MD, assistant professor at the Stanford University School
of Medicine, reported the finding at the 85th Scientific Assembly and Annual
Meeting of the Radiological Society of North America.
Birdwell, who is also acting director of the radiology residency program at
Stanford, tells WebMD "that was one of the most striking findings of our
study -- half of the tumors were in non-dense breasts." Birdwell says that
the study debunked most of the mammography lore that she believed. "I
thought that missed lesions look different, were usually calcifications or
occurred in unusual locations. In our study none of those assumptions turned
out to be true."
She and her colleagues amassed records from more than 1,000 consecutive
cases of breast cancer detected through mammogram screenings. In about half of
the cases, prior mammograms were available for comparison. A radiologist then
examined the paired mammograms and determined that in almost 300 cases,
evidence of cancer was visible on the first mammogram but had not been
identified. An expert panel of five radiologists, who were blinded to the
results of the second mammogram, were asked to review the initial films. "A
majority of the five identified 115 cancers in 110 women and recommended recall
imaging," Birdwell says. She then studied the characteristics of these
"Most of them weren't calcifications. They were masses," she says.
Eighty-two of the 115 were invasive cancers and almost half were in the upper
outer quadrant of the breast, a "very common location," she says.
Birdwell offers several theories to explain the missed diagnoses, including
a very simple one: the mammographers were too distracted by other tasks to
concentrate on the films under review. She says that at most busy breast
centers, films are reviewed in rooms that aren't dark enough and that are too
accessible to distractions from co-workers. "I've only ever seen one ideal
screening room. ... It was down a hall, away from the action, and completely
dark. I don't even think there was a phone. I was envious."
She says, too, the fact that about half the lesions were found in fatty
breasts suggests that sometimes mammographers may "let down our guard a
little when we have a fatty breast, so that's a teaching point."
Traditionally, fatty breasts are easier to detect breast cancers in than are
the denser breast tissues.
A remedy for the situation might be having two people review mammograms, and
Birdwell says that several institutions do attempt this "second read"
approach. "But this has pitfalls too, not the least of which is legal. Who
is responsible for dictating the notes? Who signs off on the case? If the first
reader is [deemed] responsible, will the second reader be attentive
enough?" she says.