Clinicopathologic Features of Prostate Cancer with Mesorectal Lymph Node Involvement on PSMA or Fluciclovine PET/CT

Abstract

Advanced PET imaging has shown more prevalent mesorectal lymph node (LN) involvement in prostate cancer than previously appreciated. The clinical features predicting risk for mesorectal involvement are not well established and the prognostic impact is unclear. This may have implications on management including radiotherapy field design. This study aims to identify clinical and pathologic characteristics associated with mesorectal involvement identified on PSMA or fluciclovine PET/CT. We conducted a single institution retrospective review of prostate cancer patients with F-18 fluciclovine, F-18 piflufolastat, or Ga-68 gozetotide PET between January 2020 and 2023 demonstrating tracer-avid mesorectal LN in the setting of newly diagnosed disease (ND) or biochemical failure after curative-intent therapy (BF). Clinical characteristics, pathologic findings, and early clinical outcomes were reviewed. We identified 16 ND and 34 BF patients with uptake in at least one mesorectal LN on PET. For ND patients, clinical features at initial diagnosis were median PSA of 35.2 (range 9.6-659), median grade group 5, and 87% with clinical or radiographic T3/T4 disease. Radiographic PET staging among ND patients (excluding mesorectal LNs) were 19% N0M0, 25% N1M0, 56% as N1M1. For BF patients, clinical features at initial diagnosis were median PSA 9.2 (range 4.1-90) and median grade group 4. Primary treatment was prostatectomy in most (91%), with a high rate of high-risk features: 68% pT3-4, 28% pN1, and 32% had persistent detectable postop PSA. Radiographic PET staging among BF patients (excluding mesorectal LNs) were 29% N0M0, 38% N1M0, 12% N0M1, and 21% as N1M1. High-risk histologic features (cribriform, intraductal, ductal, or neuroendocrine) were identified in 88% of ND and 48% BF patients. Of these patients, 86% had cribriform pattern. Median PSA prior to PET for ND and BF patients was 37.0 (range 8.5-659) and 1.9 (0.2-11.1). Median interval from initial therapy to PET for BF patients was 4.4yr (range 0.2-19.7). Median follow-up post-PET was 8.7mo (range 3.4-29) for ND and 8.8mo (range 0-76) for BF patients. Of patients with M0 PET staging, none of the 7 ND patients developed DMs, and 1 of 23 BF patients developed DM after 4 yrs. In this analysis of prostate cancer patients with mesorectal involvement, we found a high incidence of high grade, T3-4 disease, and cribriform pattern, especially in ND patients. For BF patients, there was a high incidence of pT3-4 and pN1 disease at time of initial treatment. Overall, most patients had concurrent regional nodal disease on PET. Longer follow up of clinical outcomes and comparison to high-risk patients without mesorectal LN involvement is needed to understand the prognostic significance and predictors of mesorectal LN spread. Additional studies are needed to identify patients at highest risk in whom elective coverage of mesorectal lymphatics with elective pelvic nodal RT may be warranted.