Homing in on node positive PC: surgical sampling, carbon 11 acetate, feraheme USPIO
Two talks highlighted the great changes that are giving us far greater ability to determine whether lymph nodes are positive: one was Dr. Dusing talk on different imaging techniques, especially carbon 11 acetate (C11-ACE), and the other was Dr. Myers talk that described dramatic success in using feraheme Ultrasmall Superparamagnetic Iron Oxide contrast agent high-resolution MRI (USPIO).
Dr. Dusing reviewed existing capabilities for lymph node imaging, noting uses but also shortcomings for most. However, he spoke very enthusiastically about C11-ACE imaging, emphasizing the point that his lab's comparative study of ProstaScint, which has FDA approval, with C11-ACE, which does not yet have FDA approval, showed C11-ACE to be far superior. In his study of nodal mets in 20 patients, the ProstaScint picked up only 6 positive nodes in 20 patients (30%), contrasted with C11-ACE which picked up positive nodes in 17 of the same 20 patients (85%). He stated that C11-ACE could pick up cancer even when the amount was less than 1 cm, the size threshold for pickup with a CT scan. I was impressed that the average (median) PSA for patients in the study was very low, just 1.03.
In his talk Dr. Dusing mentioned the Combidex USPIO high-resolution MRI scan that was formerly available in the Netherlands. He said that results looked good, but he noted that it was no longer available as the manufacturer of the contrast agent was no longer supplying it. Many of us had had great hopes for this scan, which had not been approved in the US.
However, in a development that is just emerging into public notice (since about April 2010), a very similar USPIO high-resolution MRI scan is now available in the US. It is based on a contrast agent, feraheme, that has already been approved by the FDA though not for prostate cancer, making the agent available for "off-label" use in scans of prostate cancer patients. The scan appears to be highly accurate - both sensitive and specific - in revealing prostate cancer in lymph nodes throughout the body. In fact, it is apparently capable of routinely spottng mets as small as 2mm, and can spot some mets as small as 1mm! Dr. Dusing did not seem aware of this scan, but that is not surprising as no paper has been published about it yet. The radiologist heading the feraheme USPIO research is Dr. Steven Bravo of Sand Lake Imaging outside Orlando, Florida, and only two doctors have been referring patients to him, Dr. Myers and Dr. Dattoli. That limited roll-out had the purposes of working out bugs and conducting careful and disciplined research that could be published. A paper is now in process.
In his own talk Dr. Myers described his clinical experience with the Sand Lake technology. He made the key point that 70% to 80% of patients he referred to Sand Lake (mostly recurring patients) turned out to have positive nodes that could be targeted by radiation, with about half of such patients achieving a PSA of 0 after receiving radiation to the nodes!
For so long we patients and our doctors could get only incomplete and somewhat doubtful information about prostate cancer in the lymph nodes. While accurate information could go a long way toward steering patients away from local therapy that was destined to be ineffective due to unrevealed nodal spread, surgical node sampling or semi-reliable imaging (such as CT scanning) were the only primary practical tools - there were no tools with high dependability. Now some really effective technology is entering the scene.
However, availability may become an issue. For C11-ACE, a new FDA safety policy threatens to shut down the cyclotron at Dr. Dusing's location that is necessary to produce the contrast agent. That is critical as the agent has a very short half-life - just twenty minutes. Dr. Dusing urged us to advocate with the FDA on behalf of the C11-ACE cyclotron. Feraheme USPIO has an advantage as the agent is already FDA approved for a different medical condition and does not face an urgent half-life problem. Dr. Myers expects that feraheme USPIO imaging will become widely available after Dr. Bravo's paper is published. Apparently any imaging facility that has 3 Tesla equipment will be able to offer it once it gets the contrast agent.
Effective lymph node imaging for prostate cancer will probably result in profound changes in prognosis (as in the Partin tables and various nomograms), in case management and treatment, and in research. I have a friend with an eleven year challenging recurrence following radiation who has now taken a shot at a cure based on feraheme USPIO imaging with follow-up targeted radiation. This is real!
This is a very helpful post - covering many of the current issues in imaging. Remember - the C11_ ACE is a PET scan. Since PET requires an injection of some type (the radioisotope), there can be different kinds of PET. FDG-18 is another. I did not hear Dr Myers' talk as I had to leave the conference on Saturday, but I hope to receive the recording soon. I appreciated Dr Dusing's talk, and his passion for patients.
This post also highlights 2 potential advocacy issues that someone might undertake: (1) the FDA & Dr Dusing's PET cyclotron issues, and (2) the emerging technology with feraheme lymph node imaging - development, FDA issues, etc. I think good advocacy looks for solutions, and strives for the win-win. It often just takes one person with a vision.
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