ORLANDO, FL, USA (UroToday.com) - Peter Pinto, MD began his talk with the caveat that, to date, the literature examining new imaging modalities in the diagnosis of early metastatic disease has been very limited. Reliable detection of occult metastatic disease is important for appropriately stratifying patients to particular treatments as well as for monitoring response to treatment. Currently used imaging modalities are inadequate to reliably detect low-volume metastatic disease.
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Dr. Pinto presented the plethora of novel PET tracers which have been recently examined for the detection of early metastatic disease. He highlighted the sodium fluoride PET which has been shown to have improved PPV and specificity when compared to traditional bone scan. While clear superiority of sodium fluoride PET over bone scan has not yet been demonstrated, it has been shown to be better than 18F-FDG PET in detecting occult metastatic disease in patients experiencing biochemical recurrence. Dr. Pinto then went on to discuss the 11C-choline PET and 18F-choline PETs, both of which hold promise given choline is upregulated in prostate cancer and may be correlated with tumor grade, Gleason score, and tumor volume. Limitations of the choline tracers, however, include the short half-life of 11C (20 minutes) which necessitates the use of an on-site cyclotron as well as the fact that choline is also taken up by BPH and requires a higher PSA for more reliable cancer detection. Dr. Pinto then quickly glossed over 11C-acetate PET, 18F-FACBC PET and 18F-FDHT (fluorodihydrotestosterone) PET, each of which have been examined in small patient series.
Dr. Pinto focused next on PSMA, a transmembrane protein whose expression is increased in prostate cancer. The ProstaScint® scan utilizes an antibody targeted to the internal domain of PSMA. In contrast, 18F-DCFBC PET utilizes a probe targeting the external domain of PSMA and has been shown to be more specific than choline or acetate PETs. Finally Dr. Pinto presented old data from 2007 looking at the use of iron oxide particles with MRI to identify patients with lymph node metastases. MRI with iron oxide was found to have increased sensitivity in comparison to traditional imaging modalities. He summarized by pointing out that while there has been, and is currently, a large amount of research looking at developing novel imaging tracers for the detection of occult metastatic disease, there is still much work to be done. To date the literature is limited and it is yet to be determined which tracers will be most effective in this setting for both diagnosis as well as treatment monitoring.
Presented by Peter A. Pinto, MD at the 2015 Genitourinary Cancers Symposium - "Integrating Biology Into Patient-Centric Care" - February 26 - 28, 2015 - Rosen Shingle Creek - Orlando, Florida USA
National Cancer Institute at the National Institutes of Health, Bethesda, MD USA
Reported by Timothy Ito, MD, medical writer for UroToday.com