A phase 2 study of 99m Tc-trofolastat chloride (MIP-1404) SPECT/CT to identify and localize prostate cancer (PCa) in high-risk patients (pts) undergoing radical prostatectomy (RP) and extended pelvic lymph node (ePLN) dissection compared to histopathology: An interim analysis.

Abstract:

Background: Technetium Tc99m trofolastat chloride is a novel small molecule SPECT radiotracer with high affinity binding to the external domain of prostate specific membrane antigen highly expressed in PCa. We conducted an open-label, multicenter study; the primary endpoint was the ability to detect PCa within the prostate gland (PG). Secondary endpoints included detection in PLNs and comparison to MRI. 

Methods: Pts with PCa scheduled for RP with ePLND at high risk (≥cT3 or nomogram score ≥130) for PLN involvement were eligible. Enrolled pts required a bone scan, pelvic MRI and received trofolastat and SPECT/CT imaging 3-6 hrs later. Readers blinded to clinical information evaluated all available image data. Results were compared to histopathology assessments of RP and ePLN surgical specimens using a common anatomic template. Target to background (T:B) ratio within the PG was measured on the SPECT/CT and compared to Gleason Score (GS). 

Results: Enrollment has been completed and interim data is available for the first 54 of 105 pts. A majority of SPECT/CT readers correctly identified the presence of primary PCa in 49/54 (91%) evaluable pts. In 47 pts who had both MR as well as trofolastat results, readers correctly identified PCa in 40/47 (85%) and 42/47 (89%), respectively. In 37 pts with no prior hormone therapy, GS following RP ranged from 3+4 to 5+5 and significantly correlated with maximum T:B values (r=0.54 p<001). In 17 patients treated with neoadjuvant hormonal therapy, T:B was significantly lower than untreated pts (p<0.005). 

Conclusions: Trofolastat SPECT/CT detected PCa within the PG in 49 of the first 54 (91%) of evaluable high-risk pts prior to surgery. Uptake of trofolastat correlated significantly with GS obtained from post-RP histopathology in untreated pts and may provide information regarding disease aggressiveness using a non-invasive technique in high-risk pts prior to surgery. Final results, analyses of secondary endpoints, pelvic lymph nodes, and comparative performance vs. MRI from this study will be presented. Clinical trial information:NCT01667536.

www.asco.org