Most of the advancements being made in the field are said to be in the form of molecular imaging, which allows for the functional and/or molecular characterization of cellular processes. Most current molecular imaging is being performed with either single-photon emission computed tomography (SPECT) or positron emission tomography (PET). Dr. Allaf’s team has led the field in the use of Tc 99m Sestamibi SPECT/computed tomography (CT) for the detection of oncocytomas. Sestamibi SPECT scans have been the imaging modality of choice for the detection of parathyroid adenomas over the last 10 years. Like the parathyroid glands, oncocytoma neoplasms have an abundant number of mitochondria, which, for unknown reasons, have a high affinity to the sestamibi molecule. In clinical practice, oncocytomas have a high uptake of the sestamibi molecule and appear “hot” in the scan; in contrast, clear cell renal cell carcinoma (CCRCC) demonstrated no uptake of the radiotracer seen as a “cold” spot in the scan. The prospectively collected institutional data were recently published by Dr. Gorin (Gorin et al. Eur Urol. 2016) showing that sestamibi SPECT/CT scans correctly identified 83% of oncocytomas, thereby resulting in an overall sensitivity of 87.5%.
With regard to the other renal histologies, carbonic anhydrase IX (CAIX) is highly expressed in the surface of CCRCC cells, and it has been used as a target for molecular imaging. Girentuximab is an IgG1 chimeric antibody designed to target CAIX, and this agent recently combined with Iodine-121 to aid in molecular imaging of CCRCC. In a study published by Divgi et al in 2013, the use of 121-I-girentuximab was evaluated, showing a sensitivity for localized and metastatic CCRCC of approximately 86%. Sadly, validation studies are lacking.
Prostate-specific membrane antigen (PSMA) has been observed to also be highly expressed in CCRCC. The group at Hopkins performed a validation trial in a patient with widely metastatic CCRCC followed by rapid autopsy. PSMA PET/CT was able to identify 53 of the 54 sites of metastatic disease previously identified with conventional CT. PSMA PET/CT noted 12 additional lesions not seen with conventional imaging. On rapid autopsy, all the lesions were confirmed to be metastatic CCRCC.
In Dr. Allaf’s conclusion, sestamibi- and CAIX-based imaging are promising modalities for the radiographic biopsy of renal tumors. PSMA-based imaging has shown encouraging results, he observed, but it still requires further validation.
Presenter: Alessandro Volpe, MD university of south piedmont, Italy
Written By: Andres F. Correa, MD, Society of Urologic Oncology Fellow, Fox Chase Cancer Center
at the 2017 Genitourinary Cancers Symposium - February 16 - 18, 2017 – Orlando, Florida USA