Maxim Rybalov

PSMA, EpCAM, VEGF and GRPR as Imaging Targets in Locally Recurrent Prostate Cancer after Radiotherapy

In this retrospective pilot study, the expression of the prostate-specific membrane antigen (PSMA), the epithelial cell adhesion molecule (EpCAM), the vascular endothelial growth factor (VEGF) and the gastrin-releasing peptide receptor (GRPR) in locally recurrent prostate cancer after brachytherapy or external beam radiotherapy (EBRT) was investigated, and their adequacy for targeted imaging was analyzed. Prostate cancer specimens were collected of 17 patients who underwent salvage prostatectomy because of locally recurrent prostate cancer after brachytherapy or EBRT. Immunohistochemistry was performed. A pathologist scored the immunoreactivity in prostate cancer and stroma. Staining for PSMA was seen in 100% (17/17), EpCAM in 82.3% (14/17), VEGF in 82.3% (14/17) and GRPR in 100% (17/17) of prostate cancer specimens. Staining for PSMA, EpCAM and VEGF was seen in 0% (0/17) and for GRPR in 100% (17/17) of the specimens’ stromal compartments. In 11.8% (2/17) of cases, the GRPR staining intensity of prostate cancer was higher than stroma, while in 88.2% (15/17), the staining was equal. Based on the absence of stromal staining, PSMA, EpCAM and VEGF show high tumor distinctiveness. Therefore, PSMA, EpCAM and VEGF can be used as targets for the bioimaging of recurrent prostate cancer after EBRT to exclude metastatic disease and/or to plan local salvage therapy.

Does Computed Tomography or Positron Emission Tomography/Computed Tomography Contribute to Detection of Small Focal Cancers in the Prostate?

Prostate cancer is considered to be a multifocal tumor in the majority of patients. Based on histologic data after prostatectomy, there is a growing insight that a considerable number of men who receive a diagnosis in the contemporary setting of prostate-specific antigen screening have unilateral or unifocal disease. With this, the current concept of whole-gland therapy has come into discussion. The need for improvement of intraprostatic tumor characterization is clear. Molecular imaging is one of the areas of research on this aspect. The clinical indications for positron emission tomography (PET)/CT have increased rapidly in the field of oncology and are largely based on fluorodeoxyglucose (FDG) PET. Both conventional CT and FDG PET, however, cannot detect prostate cancer foci <5 mm within the prostate. Dynamic contrast-enhanced CT involves imaging a region of interest rapidly (usually <10 seconds between images) during a bolus intravenous injection of a contrast agent. Through analysis of the contrast enhancement time curves, it is possible to distinguish tissues with different microvascular properties such as cancer. The technologic aspects of both imaging techniques and the clinical results of 11C-choline PET/CT for intraprostatic tumor characterization are discussed. Based on preliminary studies, dynamic contrast-enhanced (DCE)-CT may be a useful tool for localization of prostate tumors and, perhaps more importantly, quantification of therapeutic response in prostate cancer. Validation work is necessary, however, to define its accuracy and role in therapeutic paradigms such as focal therapies, particularly given the current accuracy of MRI. In the future, combining DCE-CT with CT or (11)C-choline PET/CT may be an alternative to MRI, offering a combination of quantitative parameters that may correlate to tumor prognosis as well as cancer localization for focal therapy.

11C-choline PET/CT in selection of patients for salvage cryoablation in recurrent prostate cancer.

188 Background: 11C-choline PET/CT has proven to be a sensitive technique for re-staging after radiation therapy (RT). The aim of this study was to analyze the clinical impact of 11C-choline-PET/CT in the selection of patients with biochemical recurrence (BCR) after RT for salvage cryoablation of the prostate. METHODS This prospective study was conducted between November 2006 and February 2012 on patients considered as candidates for salvage cryoablation. 74 patients, mean age 69.2 years, median - 70.3 years (range 49-79), who were being followed up after RT for histological proven prostate cancer (according to ASTRO-Phoenix) were included. Until 2009 we used PET/CT fusion, but from 2009 all patients were examined with an integrated PET/CT system. After receiving 400 MBq 11C-choline intravenously, a whole body scan was made. As reference we used biopsy-proven histology from site of suspicion, confirmative imaging modalities (bonescan, CT) or clinical follow-up. PSA doubling time and velocity was calculated. RESULTS According to the PET/CT results, 40 (54%) patients had a local recurrence, 20 (27%) had regional/distant metastases and 14 (19%) had a negative scan. The positive PET findings were proved by histology from prostate biopsies and/or pelvic lymph node dissections in 63% of cases. Considering PET/CT results: 50/74 (68%) patients received cryoablation, for 24/74 (32%) treatment was changed (active surveillance or androgen deprivation therapy). CONCLUSIONS 11C-choline-PET/CT could be useful for the selection of patients with BCR after RT for salvage cryoablation of the prostate. 11C-choline-PET/CT was decisive and led to therapy change in 32% of cases. [Table: see text].