Comparison of gallium-68- and choline-C11-based PET/CT scanning in high-risk and progressive prostate cancers

The question of how much better the varied, new forms of imaging will be in the evaluation of patients with higher-risk prostate cancer both before and after their treatment is a currently “hot topic” in the world of prostate cancer.

Here in America, there are still only as small number of centers where tests like the [11C]choline imaging test and other,comparable but investigational tests are available, and the newly approved Axumin imaging test that uses [18F]fluciclovine is yet to be widely rolled out. By comparison, in other countries, it is already reasonably easy to get various types of 68Ga-PSMA imaging test, and one of the key questions is whether any one of the 68Ga-PSMA tests might be significantly better at detection of positive lymph nodes or other, early forms of metastasis than the [11C]choline test.

A new article by Schwenck et al. (a German clinical research group) in the European Journal of Nuclear Medicine and Molecular Imaging offers us some initial insight into that question.

The authors set out, very specifically, to compare the value of the PSMA ligand 68Ga-PSMA-11 with [11C]choline in the assessment of patients with both primary and recurrent forms of prostate cancer. They carried out two whole-body PET/CT scan examinations on each of a total of 123 prostate cancer patients using both 68Ga-PSMA-11 and [11C]choline.

Here is what they report:

  • 103/123 patients (84 percent) were patients who had a confirmed biochemical relapse after prostatectomy and/or radiotherapy (with a mean PSA level of 4.5 ng/ml).
  • 20/123 patients (16 percent) underwent primary staging prior to any treatment.
  • 458 lymph nodes suspicious for metastasis were identified in 67/103 patients with biochemical relapse.
  • Compared to the PET/CT scans using [11C]choline, PET/CT scans using 68Ga-PSMA-11
    • Had a higher uptake and detection rate for these suspicious lymph nodes
    • Identified significantly more patients with suspicious lymph nodes
    • Were able to identify affected lymph nodes especially well at low PSA levels.
  • Bone lesions suspicious for prostate cancer metastasis were revealed in 36/103 patients with biochemical relapse.
  • Among these 36 patients
    • Just 3 patients (8 percent) had only 68Ga-PSMA-11-positive bone lesions (i.e., without any sign of positive lymph nodes).
    • Significantly more bone lesions were detected by 68Ga-PSMA-11 PET/CT scanning than by [11C]choline PET/CT scanning.
    • Just 2 patients presented with bone lesions that were detected exclusively by 68Ga-PSMA-11 PET/CT scanning.
  • [11C]choline PET/CT scans detected 29 suspicious lymph nodes and 8 bone lesions that were not identified using 68Ga-PSMA-11 PET/CT scans.
  • Among the 20 patients who underwent initial staging, prior to any treatment, all primary tumors showed uptake of both tracers.
  • These findings led to crucial differences in the TNM classification and the identification of oligometastatic patients.

The bottom line, based on this set of 123 patients at this institution, appears to be that 68Ga-PSMA-11 PET/CT scans are able to detect the presence of suspicious lymph nodes more often than [11C]choline PET/CT scans, but that the [11C]choline PET/CT scans can detect at least some suspicious lymph nodes and some bone metastases that are not evident based on a 68Ga-PSMA-11 PET/CT scan.

Data like these will certainly help us to carry out better tests to identify patients with N+ and M+ disease earlier in their disease process and to adjust for this in considering the most appropriate forms of treatment for such patients as early as possible. On the other hand, it is disappointing that there seem to be a small but significant number of suspicious lymph nodes and bone mets that do not seem to show up on the 68Ga-PSMA-11 PET/CT scans.

One Response

  1. As I understand it, there is a crucial difference between these two types of scan: the C-11 scan is a metabolic scan, so will tend to highlight faster growing metastases. The Ga-68 scan detects expression of the PSMA protein, no matter how fast the cancer is growing. So I am not surprised that [11C]choline detects some metastases that do not show up on [68Ga]PSMA. If I had rising PSA but a negative Ga-68 scan, I would want to follow through with a metabolic scan, such as [11C]acetate, [11C]choline, or Axumin.

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