[ RadSafe ] Article; PET/CT shows potential for detecting unknown primary cancers

John Jacobus crispy_bird at yahoo.com
Fri Dec 9 07:42:49 CST 2005

>From a news service I belong to.  Note that each
subject already had a cancer or was treated for a
secondary lesion.

I heard that the typical PET/CT scan was about $3,000

The original is at

PET/CT shows potential for detecting unknown primary
By: Jonathan S. Batchelor

Detecting the primary lesion in patients presenting
with cancer and an unknown primary is one of the more
demanding tasks in diagnostic medical imaging. It's
imperative that the primary be identified so that the
patient can receive therapy that is adequate for the
malignancy. Generally, the most common unknown primary
cancers are adenocarcinoma, squamous cell carcinoma,
and poorly differentiated carcinoma.

At the recent RSNA conference in Chicago, a pair of
presentations put PET/CT to the task of detecting
unknown primary cancers. Dr. Mehmet Öksüz from the
department of radiology at the Katharinen Hospital in
Stuttgart, Germany, investigated the impact of
coregistered F-18 FDG-PET/CT imaging on the
identification and exact anatomic localization of
primary tumors.

"One of the major disadvantages in the past was the
lack of exact anatomic localization of F-18 FDG-PET
foci, leading to several false-positive findings,"
Öksüz said.

His research team evaluated 87 consecutive F-18
FDG-PET/CT exams of 43 patients with metastatic
cervical adenopathy and 44 patients with extracervical
metastases. The scans were conducted on a Discovery LS
PET/CT system (GE Healthcare, Chalfont St. Giles,
U.K.) one hour after intravenous injection of 360 MBq
of F-18 FDG. 

According to Öksüz, the group assessed whether a
possible primary tumor could be identified by PET or
only in the fused images of the PET/CT system. The
team also sought to determine if the localization of
lesions by CT contributed to therapeutic management.

Öksüz said that a possible primary tumor, determined
by F-18 FDG foci, was detected in 35 cases, or 42% of
the cohort. In 21 of these cases, nontumor-like
lesions were found in the PET/CT images. However, in
the remaining 14 cases tumor-like lesions were
depicted and histologically identified as five ear,
nose, and throat (ENT) tumors; two gastric wall
tumors; two cases of thyroid cancer; and one case each
of cancer of the esophagus, mandible, breast, ovary,
and kidney. 

In the 14 patients with primary lesions, nine had
disseminated FDG foci, observed Öksüz. He added that
in four of these nine patients, the PET/CT images
showed potential local complications, which needed
additional therapeutic measures. Overall, the
researchers' use of PET/CT allowed them to definitely
identify 16% (14 of 87 patients) of the primary
lesions in cancer of unknown origin.

Öksüz attributed the success to capability of the
PET/CT system to precisely localize pathological F-18
FDG uptake via its CT component. He said that this
made the histological verification by biopsy easier
for the clinicians, particularly in complex anatomic
areas such as the ENT region.

In the second RSNA presentation, Dr. Stefano Fanti,
from the nuclear medicine department, PET unit, at the
Policlinico S. Orsola-Malpighi in Bologna, Italy,
presented the results of a study carried out to
evaluate the role of FDG-PET/CT for detecting unknown
primary cancer in patients with biopsy-proven
secondary lesions.

His group's study population consisted of 36 patients,
14 female and 22 male with a mean age of 64.5 years.
All the patients had at least one biopsied secondary
lesion, a negative physical examination, and negative
or inconclusive conventional imaging tests performed
on modalities such as CT, ultrasound, or MR.

Fanti said that 15 of these patients had
adenocarcinoma; seven patients had a nondefined
epithelial carcinoma, six had squamous cell carcinoma,
two were determined to have poorly differentiated
carcinoma, and one patient each had transitional cell
carcinoma, a germ cell tumor, a flat cell tumor,
melanoma, a spinocellular carcinoma, and a spindle
cell carcinoma. 

Each patient underwent a FDG-PET/CT scan on a
Discovery LS PET/CT and their results were evaluated
by the team, according to Fanti.

The Italian team showed that in 44% of the patients,
17 cases, PET/CT detected the primary occult lesion.
This was found in the lung of seven patients, the
tongue of two patients, and one each in the testis,
tonsil, ovary, biliary system, colon, hypopharynx,
tongue, and pharynx of the remaining patients. 

In one case, noted Fanti, PET/CT detected an equivocal
gastric hypermetabolic area consistent with primary
lesion but, as gastroscopy was negative, this finding
was not considered definitive. 

In 53% of the patients, 18 cases, PET/CT was not
conclusive for detecting the primary occult lesion, he

Fanti, like Öksüz, attributed the team's success to
detecting unknown primary lesions to the utilization
of PET/CT.  

"This may be due to the correlation of metabolic data
provided by the PET scan and the morphological data
provided by CT attenuation correction, making it
easier for the reader to study anatomically
complicated areas such as the head, neck, pelvis, and
abdomen," he said.

By Jonathan S. Batchelor
AuntMinnie.com staff writer
December 8, 2005

"Efforts and courage are not enough without purpose and direction."
"John F. Kennedy, U.S. President and former Naval Officer 

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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