In
patients who have neurologic
symptoms indicative of cancer,
whole-body positron emission
tomography-computed tomography
(PET-CT) may improve the detection
rates when other screening test
results are negative, researchers
say.
The use of PET-CT increased the
diagnostic yield for cancer by 18%
in patients with suspected
paraneoplastic neurologic
disorders for whom results of
standard oncologic tests were
negative, Andrew McKeon, MB, MRCPI,
of the Mayo Clinic in Rochester,
Minn., and colleagues reported
online in Archives of
Neurology.
"This is important in that
firstly, cancer is detected,"
McKeon said in an interview with MedPage
Today. "The cancers were
treated in all patients and seven
of 10 patients went into
remission. In addition, five of 10
had improvements in neurologic
problems through cancer treatment
or treatment with immunotherapies."
Paraneoplastic neurologic
disorders occur in some people
with cancer -- including lung,
breast, or ovarian cancer -- and
develop when cancer-fighting
antibodies mistakenly attack cells
in the nervous system.
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that PET-CT increased the
diagnostic yield for cancer
by 18% in patients with
suspected paraneoplastic
neurologic disorders for
whom results of standard
oncologic tests were
negative.
Routine
screening for cancer in patients
with such symptoms -- including
physical examination, CT of the
chest, abdomen and pelvis, and
mammography or testicular
ultrasound -- may be unrevealing.
That's often because cancers
detected in a paraneoplastic
context are frequently small and
restricted to one site.
Detecting
autoantibodies via serologic
testing refines the search and
detects cancer in about 70% of
seropositive patients, the
researchers wrote.
"Once
[a paraneoplastic antibody] is
detected and the suspicion is
raised for underlying cancer, the
challenge is to try and find
it," McKeon said. "So we
wanted to try and see what sort of
patients we would find cancers in
with PET-CT and try and predict
what type of patients the cancers
would be found in."
PET-CT
allows the detection of
radiolabeled fludeoxyglucose
preferentially taken up by highly
metabolically active cancers.
To
evaluate its ability to detect
cancer, the researchers conducted
a literature review for studies
that evaluated the utility of PET
for cancer diagnosis in patients
with paraneoplastic neurologic
disorders. Then they did a
retrospective review of medical
records of 56 patients with
clinically suspected
paraneoplastic neurologic
disorders who'd had PET-CT scans
after standard evaluations that
turned out to be negative.
Median
age of the patients at symptom
onset was 61.
Before
their PET-CT, patients had had a
median of three other screening
tests; the most common was CT of
the chest, abdomen, and pelvis.
Using
PET-CT, the researchers detected
abnormalities suggestive of cancer
in 22 patients, or 39% of the
total population.
Among
these, cancer was confirmed
histologically in 10 patients as
follows:
- Thyroid
papillary cell carcinomas: 2
- Solitary
lymph nodes: 2 adenocarcinomas,
1 small cell carcinoma
- Tonsil
squamous cell carcinoma: 1
- Lung
carcinomas: 1 adenocarcinoma,
1 small cell, 1 squamous cell
- Colon
adenocarcinoma: 1
All
10 patients were seropositive for
paraneoplastic autoantibodies.
Four
of the 10 cancers detected using
PET-CT were outside the anatomical
scope of CT of the chest, abdomen,
and pelvis. The six other cancers
were too small to be detected by
an appropriate regional CT, the
researchers wrote.
Among
the other 12 patients who had
abnormalities on PET-CT, two had
premalignant lesions, one had a
noncaseating granuloma, five had
negative biopsy results, and other
PET-directed evaluations without
biopsy were negative in two. There
were no further evaluations in the
remaining patients.
The
researchers found that detection
of a well-characterized neuronal
nuclear or cytoplasmic
paraneoplastic autoantibody was
associated with a successful
PET-CT-directed cancer search (P<0.001).
Since
the majority of cancers were
detected in a limited-stage, 70%
of treated patients went into
remission. Five patients had
sustained improvements in
neurologic symptoms after a median
follow-up of 11 months.
Based
on their literature review, the
present study had a higher
detection rate of cancer for
PET-CT (12% versus 18%), which may
be explained by a larger number of
patients available for follow-up
in the present study or the
enhanced sensitivity of PET-CT
over PET alone.
Still,
a caveat is the screen's high
false-positive rate.
"PET-CT
is very sensitive, since it can
pick up hypermetabolic
tissue," McKeon said.
"But tissue can be
hypermetabolic for different
reasons."
He
added that PET-CT "is by no
means the be-all and end-all of
this. It's just a helpful
screening tool in patients where a
cancer is suspected."
They
acknowledged that their study was
limited by its retrospective
design and small sample size, but
the researchers concluded that
"recognizing the limitations
of PET-CT, we favor this modality
for initial oncologic evaluation
of patients in whom a
paraneoplastic neurologic disorder
is strongly suspected."
A
co-author stands to receive
royalties for commercial assays
to detect aquaporin-4-specific
autoantibodies.
The
other researchers reported no
conflicts of interest.
