San Francisco—C-11 choline positron emission tomography (PET) and multiparametric pelvic magnetic resonance imaging (pMRI) can be used successfully to identify recurrence patterns in patients with biochemical recurrence after radical prostatectomy.
Use of such imaging shows a low rate of local-only recurrence at a median PSA level of 2.3 ng/mL but a higher than anticipated frequency of metastatic recurrence, reported researchers from Mayo Clinic, Rochester, MN.
At the Genitourinary Cancers Symposium in San Francisco, they presented data from a cohort of 260 men evaluated with choline PET and pMRI for suspected prostate cancer relapse after prostatectomy.
Despite the high rate of distant recurrence in the cohort studied, two-thirds of patients had disease limited to the pelvis, making them potential candidates for local therapies, including salvage radiation, said Ilya Sobol, MD, a Mayo Clinic urology resident working with Eugene D. Kwon, MD, and colleagues.
C-11 choline PET uses choline C-11 as a tracer, which is taken up rapidly by prostate cancer cells prior to PET imaging, which detects the location of tracer concentrations. C-11 choline PET has been used in Europe for more than 10 years to detect recurrent prostate cancer, and now has been surpassed by even more accurate imaging techniques such as (68)Ga-labeled PMSA scan, which is not currently approved by the FDA.
“It is able to detect recurrent prostate cancer, particularly in soft tissue and in bone, much better than anything else we’ve had before,” Dr. Sobol said.
Between 2008 and 2015, 2,466 men were evaluated at Mayo Clinic with choline PET and pMRI for suspected prostate cancer relapse. From this cohort, 260 patients who underwent prostatectomy alone without adjuvant or salvage therapy were identified and were imaged simultaneously with choline PET and pMRI. Of these, 202 (78%) had some form of positive imaging that was confirmed subsequently.
Suspected radiographic relapse was confirmed by pathologic sampling in 44%, continued rising PSA and lesion progression on successive imaging in 5%, or decline in PSA accompanied by lesion regression in response to therapy in 51%.
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Based on historical data, the time from biochemical recurrence to identification of metastases using bone scans is about 8 years, said Dr. Sobol.
Oligometastatic states of disease
“The idea behind our study is that there must be states of disease that are oligometastatic, but we just haven’t been able to see it,” he said. “We have a very unique pure cohort of patients that had a prostatectomy and a PSA recurrence but refused empiric treatment. Eventually, their PSA rose to a median of 2.3 ng/mL, at which time they received multiparametric pMRI and a C-11 choline PET, which in the U.S. now is the most accurate restaging you can do for a patient with a PSA recurrence after prostatectomy.”
The median PSA levels for patients with local only recurrence, local recurrence plus distant disease, and distant metastasis only were 2.3 ng/mL, 2.6 ng/mL, and 2.2 ng/mL, respectively. The median interval from biochemical recurrence to a positive scan was 33.5 months in those with local recurrence only, 15 months in those with local recurrence with metastasis, and 7 months in those with metastasis only.
When the location of the disease was mapped, 33% were found to have pure local recurrence and 20% had pelvic lymph node recurrence only.
“We had only 9% who had local recurrence and pelvic lymph node metastases,” Dr. Sobol said. Four percent had peri-rectal lymph node recurrence with or without other pelvic-only disease.
Imaging revealed that 33% to 66% of the cohort would have all sites of disease treated by salvage radiotherapy, depending on the extent of the treatment field.
The current understanding of recurrent prostate cancer is dichotomized into local recurrence or distant metastasis, in which patients receive radiation for local recurrence or hormonal therapy for distant metastasis, Dr. Sobol said.
He believes that knowledge of oligometastatic states with advanced imaging techniques may drive decision-making with respect to the timing of radiation and the proposed radiation field, or whether to offer radiation at all to patients who have a low chance of success.
“The answer is not going to be 8 years from now with a bone scan,” he said. “It’s going to be 7 months from now or 15 months from now with an MRI.”
One study co-author is a consultant/adviser for Bayer Schering Pharma and Piramal Life Science and has received research funding from AVID Radiopharmaceuticals, GE Healthcare, and Siemens Healthcare Diagnostics.
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