PET/MRI scanning in pre-surgical staging of high-risk prostate cancer patients

A small, Norwegian, Phase II clinical trial has explored the potential diagnostic value of [18F]fluciclovine PET/MRI scans of the pelvic lymph nodes in staging for patients with high-risk prostate cancer.

Selnæs et al. have reported data from 28 patients who were given [18F]fluciclovine (Axumin) PET/MRI scans immediately prior to their surgery.

The data from the PET/MRI scans were then compared (on a region to region basis) with the data from actual lymph nodes surgically removed from eight pre-defined regions of the pelvis.

Here is a summary of the study findings:

  • Patient-based sensitivity and specificity for detection of pelvic lymph node metastases were
    • 40.0 and 87.5 percent, respectively, based on MRI data
    • 40.0 and 100.o percent, respectively, based on PET data
  • Region-based sensitivity and specificity for detection of pelvic lymph node metastases were
    • 35.0 and 95.7 percent, respectively, based on MRI data
    • 30.0 and 100.0 percent respectively, based on PET data
  • The sizes of true lymph node metastases (found at surgery) in true-positive regions were significantly greater than metastases in false-negative regions.
  • PET scan-positive pathologic stage N1 patients had higher metastatic burdens than PET scan-negative N1 patients.

The authors conclude that:

Simultaneous [18F]fluciclovine PET/MRI provides high specificity but low sensitivity for detection of [lymph node] metastases in high-risk prostate cancer patients.

However, they also make the following additional “key points”:

  • [18F]Fluciclovine PET/MRI
    • Has high specificity for detection of lymph node metastasis
    • Lacks sufficient sensitivity to replace extended pelvic lymph node dissection
    • May be used to aid surgery and select adjuvant therapy
  • [18F]Fluciclovine PET-positive patients have more extensive disease than PET-negative patients.
  • The size of metastatic lymph nodes is an important factor for detection.

Based on the low level of sensitivity of Axumin PET/MRI scans in the pre-surgical detection of pelvic lymph nodes, it seems unlikely (based on these data) that this methodology has a current role in the pre-surgical staging of most high-risk prostate cancer patients, but there may be exceptional cases in whom it would have utility. Whether any payer here in the USA would cover the cost of this agent when used in this manner is a whole other question.

One Response

  1. The use of pelvic lymph node dissection has long been a key element of pathological staging for pTNM status. It had been hoped that extended pelvic lymph node dissection (epLND) would help, but the complications of ePLND are significant and there has been no evidence of a survival benefit to date. I believe that places limits on the real value of precise staging of N status. However, choline PET/CT and other forms of imaging can certainly detect bone metastases obviously not found with PLND. That might help patients to get appropriate treatment. But that was not the issue for this report.

    Most studies so far have used PET/CT so the issue for the Norwegian study was whether the PET/MRI might be better than PET/CT. It would not be possible to prove that in a small single-arm cohort study.

    It is well known that imaging with PET has a limit of size for detection of any type of metastasis. So men with PET scan-positive lymph nodes might have a worse prognosis than PET scan-negative lymph nodes but that was also not the topic in this report.

    I agree with the conclusion the study would not change routine management. However, that does not mean that new imaging does not help management. We have increasing numbers of reports where salvage radiation therapy and lymph node removal is carried out on the basis of PSMA-based PET/CT scans. But PSMA-based PET/CT is not available in many countries.

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