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Flat Colon
Lesions common, linked to Colorectal Cancer
Newswise — Flat, non-polypoid
colorectal neoplasms (NP-CRNs), which may be
difficult to detect, appear to be relatively
common and may have a greater association
with cancer compared with the more routinely
diagnosed type of colorectal polyps,
according to a study in the March 5 issue of
JAMA.
Colorectal cancer is
the second leading cause of cancer death in
the United States. Prevention has focused on
the detection and removal of polypoid
(resembling a polyp) neoplasms (a new and
abnormal growth). Recent studies, however,
have demonstrated that colorectal cancer can
also arise from NP-CRNs.
“Nonpolypoid colorectal
neoplasms are more difficult to detect by
colonoscopy or computed tomography
colonography because the subtle findings can
be difficult to distinguish from those of
normal mucosa [membrane].
"As compared with
surrounding normal mucosa, NP-CRNs appear to
be slightly elevated, completely flat, or
slightly depressed,” the authors write. Data
are limited on the significance of NP-CRNs.
Roy M. Soetikno, M.D.,
M.S., and colleagues with the Veterans
Affairs Palo Alto Health Care System, Palo
Alto, Calif., examined data from a group of
1,819 patients undergoing elective
colonoscopy to estimate the prevalence of
NP-CRNs and to characterize the association
of NP-CRNs with colorectal cancer.
The overall prevalence
of NP-CRNs was 9.35 percent (n = 170). The
prevalence of NP-CRNs in the subpopulations
for screening, surveillance, and symptoms
was 5.84 percent, 15.44 percent, and 6.01
percent, respectively.
The overall
prevalence of NP-CRNs with cancer that had
not spread or had spread in tissue beneath
the mucous membrane was 0.82 percent; in the
screening population, the prevalence was
0.32 percent. Overall, NP-CRNs were nearly
10 times more likely to contain cancerous
tissue than polypoid lesions, irrespective
of the size.
The positive
size-adjusted association of NP-CRNs with
cancer that had not spread or had spread in
tissue beneath the mucous membrane was also
observed in subpopulations for screening and
surveillance.
The depressed type of
NP-CRNs had the highest risk (33 percent).
Nonpolypoid colorectal neoplasms containing
cancer were smaller in diameter as compared
with the polypoid ones.
“In conclusion, in this
population of patients at a single Veterans
Affairs hospital, NP-CRNs were a relatively
common finding during colonoscopy.
"They
were more likely to contain carcinoma
compared with polypoid neoplasms,
independent of lesion size. Recent studies
have pointed out differences in the genetic
mechanisms underlying nonpolypoid and
polypoid colorectal neoplasms.
"Future
studies on NP-CRNs should further evaluate
whether the diagnosis and removal of NP-CRNs
has any effect on the prevention and
mortality of colorectal cancer and
particularly focus on their genetic and
protein abnormalities,” the authors write.
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