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More on PET scans and their role in prostate cancer detection

Posted Jan 02 2010 12:00am

A few days ago we suggested that the role of positron emission tomography (PET scanning) as a diagnostic and prognostic tool in patients with prostate cancer was probably best limited to research studies at major medical centers at the present time. A recent study from Germany appears to confirm this suggestion.

Steuber et al. have reported data from a study designed specifically to evaluate the diagnostic potential of PET/CT scans using the agent [18F]fluorethylcholine (FEC) to identify positive lymph nodes (LN) in men with high-risk prostate cancer prior to a radical prostatectomy (RP) with lymph node dissection.

The authors enrolled 20 patients with localized prostate cancer and at least a 20 percent probability of having positive lymph nodes (clinical stage TxN+) according to a published nomogram. In each case the PET/CT was done 14 or more days after the prostate biopsy. Subsequently, all 20 patients received an open RP and an extended pelvic LN dissection (ePLND).

The authors assessed the patients’ clinical stage, PSA level, and biopsy Gleason score prior to surgery and a complete histopathological evaluation of the RP specimens and the dissected lymph nodes was carried out. The results from the PET/CT scans were then compared with the anatomical positions of lymph node metastases actually found at the time of dissection. The results of the study showed the following:

  • A total of 285 lymph nodes were removed from the 20 patients, with a mean number of 15 nodes per patient (range, 7 to 26).
  • 9/20 patients (45 percent) were lymph node positive.
  • These 9 patients had a total of 31 positive lymph nodes, with a mean size of 7 mm (range, 0.8-12 mm).
  • Positive lymph nodes were found in the obturator fossa (11/31, 36 percent), the external iliac artery/vein (15/31, 48 percent), and the internal iliac artery/vein (5/31, 16 percent).
  • FEC-based PET/CT did not detect even one single positive lymph node in these 20 patients, and thus gave false-negative results in 9 patients with 31 metastases and true negative results in another 254 cases.

At about $3,000 to $6,000 for each PET scan, that’s a pretty expensive way to fail to identify positive lymph nodes 100 percent of the time!

 The authors conclude, straightforwardly, that FEC-based PET/CT scanning “did not prove to be useful for [lymph node] staging” in patients with high-risk, localized prostate cancer prior to treatment and should not be used as a diagnostic tool even when clinically occult, metastatic disease is suspected.

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