Castration-resistant prostate cancer (CRPC) on PSMA-PET: Imaging features, disease distribution, and a comparison to castration-sensitive prostate cancer (CSPC).

Abstract

e17062 Background: 18F-DCFPyL PET/CT is increasingly used in the staging and response assessment of patients (pts) with prostate cancer. Recent studies suggest that short-term ADT increases prostate-specific membrane antigen (PSMA) expression, whereas long-term ADT suppresses PSMA. Changes in PSMA expression after the development of CRPC are uncertain. We described 18F-DCFPyL PET findings in pts with CRPC and compared them to findings in CSPC. Methods: We analyzed 538 18F-DCFPyL scans performed at our large academic center. CRPC was defined as rising PSA w/ testosterone < 50 ng/dL on ADT. M0 CRPC was defined as absence of extra-pelvic disease (dz) and oligometastatic CRPC (oCRPC) was defined as ≤ 5 LN + osseous lesions and absence of visceral dz. Highest SUV max (hSUVmax) was abstracted from radiologist impression. Means between groups were compared using two-tailed t-tests; undetectable PSA levels were scored as “0”. Logistic regression was used to compare dz distribution between castrate states. Significance was defined as p < 0.05. Results: There were 81 pts with CRPC, 72 pts with metastatic CRPC (mCRPC) and 123 pts with mCSPC. The median ages of pts with mCRPC (74.5 years) and mCSPC (71) were similar. The mean PSAs of mCSPC (20.2 ng/mL) and mCRPC (69.4) were significantly different. hSUVmax was higher in mCRPC (mean 40.3, 95% CI 32.7 – 47.8) than in mHSPC (22.6, 18.4 – 26.9), p < 0.001. Distribution of mCRPC lesions was as follows: prostate bed (26.4%), local pelvic LN (25%), distant LN (M1a, 41.7%), osseous (M1b, 16.7%), and visceral (M1c, 16.7%). In a multivariate analysis mCRPC pts had lower rates of pelvic LN dz and higher rates of M1c, with a trend toward increased M1b (p < 0.10), compared to mCSPC pts. ADT and androgen pathway inhibition did not affect hSUVmax in CRPC. Within CRPC, there were 9 pts with M0 dz, 24 pts with oCRPC, and 48 pts with polymetastatic dz (pmCRPC). The ages (Table) of pmCRPC and oCRPC pts were similar. The mean PSA of pmCRPC (100.9) was higher than that of oCRPC (8.8) and M0 CRPC (5.7). hSUVmax between oCRPC (40.3) and pmCRPC (40.3) was similar. Conclusions: The greater hSUVmax in mCRPC may implicate the effect of ADT on PSMA expression or may describe differing tumor biology. mCRPC pts had less local dz and more frequent distant metastases, likely reflecting more advanced disease. These findings will help inform detection of developing castrate resistance on PSMA-PET. More data are needed on the classification of oligometastatic dz on PSMA-PET and the impact of hormone therapy on PSMA in CRPC. [Table: see text]