The accuracy of [11C]choline PET/CT scans in actual clinical practice


Although [11C]choline PET scans have been a “hot” developing tool for the identification of sites of recurrence of prostate cancer after first-line treatment, we have few data as yet confirming the accuracy of these scans through pathology.

According to a newly published paper from an Italian research group, the positive predictive value (PPV) of an [11C]choline PET/CT scan in correctly identifying patients with a single positive lymph node at salvage lymph node dissection is poor — at just 24 percent.

Passoni et al. set out to conduct a pilot study to assess the accuracy of [11C]choline PET/CT scanning as a way to identify and subsequently remove a single positive lymph node through lesion-targeted salvage lymph node dissection. To do this, they looked at data from a limited number of men with biochemical recurrence after  first-line surgery and a single positive spot on a [11C]choline PET/CT scan who were then given a pelvic or a pelvic and retroperitoneal lymph node dissection as salvage surgery.

Here are their findings:

  • The study included 46 patients who met the enrollment criteria.
  • 30/46 patients (65 percent) actually had positive lymph nodes at pathologic examination of the excised tissues.
  • Of these 30 patients
    • 16 (i.e., 16/46 or 35 percent) had pathologically confirmed metastases in the same lymphatic region as shown on their [11C]choline PET/CT scan.
    • 11 (i.e., 11/46 or 24 percent) had involvement of a single lymph node.
  • 28/46 men (61 percent)  had positive lymph nodes in other areas after lymphadenectomy.
  • 8/46 men had no evidence of metastasis after lymphadenectomy.
  • The overall PPV of [11C]choline PET/CT scanning was
    • 34.8 percent when exact concordance was defined according to the lymphatic region sampled.
    • 23.9 percent when exact concordance was defined according to the single positive lymph node identified on PET/CT scanning.
  • The PPV was different for men who had or or had not been given any form of androgen deprivation therapy (ADT).
    • For men who had received ADT, the PPV ranged from 33.3 to 44.4 percent.
    • For men who had not received ADT, the PPV ranged from 17.9 to 28.6 percent.

The authors point out that, as a consequence, they do not feel able to rely on [11C]choline PET/CT scan data to accurately identify lymph nodes that can be excised through salvage lymphadenectomy. Rather, a more extensive form of salvage treatment is necessary in their patients to maximize the possibility of curative excision of cancer-positive lymph nodes.

Although these data are from a single center, it is clearly going to be disappointing if the real accuracy of [11C]choline PET/CT scan data in the identification of cancer-positive lymph nodes and other tissues is this low. We may need to watch with care for analogous, prospective data from other centers before it becomes clear just how good [11C]choline PET/CT scanning is as a means to detect micrometastases that can be treated with curative intent.

9 Responses

  1. Don’t you think it would be a mistake for a patient to view a prospective lymphadenectomy with curative intent, based on a [11C]choline PET/CT scan (or other scan for that matter)? If there is micrometastasis, what are the odds that the prostate cancer cells are actually only located (as opposed to detectable by scan or even pathology) in one lymph node? Thanks.

  2. Richard:

    On the basis of these data … yes. However, it has certainly been the case that one of the rationales behind the development of newer forms of imaging like the [11C]choline PET/CT scan has been that such imaging might well allow for treatments like salvage lymphadenectomy and targeted salvage radiation therapy to be carried out with curative intent.

  3. Do we know when comparable data might be published on the [11C]acetate imaging?

    A year ago, I compared results from [11C]choline, the tracer this post focuses upon, and results from preliminary studies of [11C]cacetate imaging done at AMIC (Arizona Molecular), and found the latter much more persuasively accurate. But surely the field has marched on farther since then.

  4. UNDER-DETECTION BY LYMPHADENECTOMY ISSUE — THE PROSTASCINT EXPERIENCE

    Based on what I recall as happening with ProstaScint scanning, I suspect that some, perhaps many of the scan-indicated lesions that were not confirmed would have grown and been found if more time had passed, especially with more aggressive cancer.

    In other words, tissue excision to confirm scan results did not find the cancerous spot in a portion of instances, but cancer later recurred. I’ve taken a brief look at positive predictive value research on ProstaScint, using PubMed, but could not spot the results I think I’m recalling accurately.

    Does anyone have a better take on what happened with ProstaScint and how it would bear on the current study?

  5. SPECULATING ON REASON FOR GREATER ACCURACY IN THE ADT TREATED GROUP

    The nature and timing of the ADT are not described in the abstract. I’m making a huge assumption that the ADT was neo-adjuvant — prior to the surgery, but not continuing post surgery.

    I’m thinking the use of ADT would be associated with more aggressive cancer prior to surgery and presumably after for the men who were not cured, and that faster growing cancer in recurrence would have been easier to detect by scan and lympadectomy, which could have led to greater success in confirming the scan results.

    Whatever the truth here, the overall results in this study are not encouraging.

  6. Hi Paul. … Sorry, I have no idea. … The people developing and applying these types of test seem to me to be less than compulsively focused on high quality data establishing their clinical value. Rather, they are doing what they need to do to get approval to use the tests.

  7. Dear Jim:

    I am far more worried by the fact that this study shows that pathologic examination of tissue post-lymphadenectomy was finding cancer that was not identified on the PET/CT scan than I am by the fact that some of the lesions identified by the PET/CT scan were not evident on pathologic examination.

    Having said that, I think the quality of imaging (and therefore the ability to accurately identify specific lesions at the time of surgery and therefore at pathology) has been vastly improved over the years since the ProstaScint test first became available. Experienced uropathologists at a major research center (which this one in Italy is) should certainly be able to see cancer tissue in surgically extracted lymph nodes if cancer is there in an amount detectable on a PET/CT scan.

  8. Jim:

    I would tend to disagree with you about the ADT. My bet would be that this ADT was given primarily to a subset of men who were seen to be at high risk at the time of surgery and who therefore received ADT after surgery (and possibly prior to scheduled radiation therapy). The only way to know would be to look at the full text of the original paper or ask the authors.

  9. Sitemaster, you wrote: “I am far more worried by the fact that this study shows that pathologic examination of tissue post-lymphadenectomy was finding cancer that was not identified on the PET/CT scan….”

    Me too. Thanks for your replies.

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