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History:
A patient with carcinoma of the right breast was referred to Main
Street Radiology for staging.
Findings:
Chest CT was performed at MSR on a 16 detector spiral CT (Figure 1). A
3 cm right axillary lymph node was noted (thin arrow). A sub-centimeter
right internal mammary lymph node is also seen (thick arrow).
A PET scan was performed (Figure 2)
showing abnormal increased metabolic activity in the right axilla
(thin arrow) and in the right internal mammary lymph node region
(thick arrow).
Fusion of PET with CT (Figure 3)
confirms that the small right internal mammary lymph node (thick
arrow) as well as the larger axillary node (thin arrow) is
hypermetabolic, consistent with metastatic disease.
Discussion:
Traditional staging of breast cancer
has often included CT of the Chest, Abdomen and Pelvis, bone scan, and
sentinel node biopsy. CT and bone scans, however, do have limitations.
Lymph nodes are commonly seen on CT.
Thus, the suspicion for tumor involvement is usually only raised on CT
when these nodes are enlarged (typically at least 1 cm). Raising
suspicion in smaller lymph nodes on CT, while increasing sensitivity,
would lead to an unacceptable specificity for malignancy. With higher
specificity, however, PET scanning can demonstrate malignancy in these
smaller nodes [5-10 mm], as seen in this case in a right internal
mammary lymph node.
Bone scans are, in actuality, 'calcium
scans.' The radioactive tracer used in bones scans localizes to
calcium, which is typically laid down in greater abundance in the bone
cortex adjacent to sites of metastatic disease in the bone marrow.
However, bone scans have difficulty detecting sites of metastatic
disease that are solely in the bone marrow and do not induce a
significant reaction. PET scans have been shown to be more sensitive
for these lesions. Several reports have noted that PET scans may be
less sensitive for blastic lesions compared to bone scans, and thus
these two studies are currently seen as complimentary.
Thus, PET scanning improves the
diagnostic accuracy of the staging of breast cancer, mostly through
its detection of distal disease. Sentinel node biopsy is still the
best method to stage the axilla.
A survey of 50 referring physicians at
UCLA revealed that PET imaging altered breast cancer patient
management by changing the clinical stage in 36% of patients, usually
by upstaging [J Nucl Med 2001 Sep;42:1334-7].
PET is approved by Medicare and most
other insurance companies, for the staging of distal metastasis from
breast cancer as well as the restaging of breast cancer with
local/regional recurrence or metastatic disease. PET is also approved
by Medicare for assessing the response of breast cancer with locally
advanced or metastatic disease after the 1st cycle of chemotherapy.
Unlike many other facilities in which
PET scan are interpreted by nuclear medicine physicians without
general radiology training, the PET scans at MSR are interpreted by
physicians boarded by both the American Board of Radiology as well as
the American Board of Nuclear medicine. Our PET center also has the
distinction of having performed the first PET scan in Queens.
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