Introduction:

IsoPSA is a structure-based assay that has been previously shown to outperform concentration-based prostate specific antigen (PSA) and free-to-total PSA ratio in detecting clinically significant prostate cancer (grade group 2 or greater) at the time of biopsy (Stovsky, Klein 2019). Thus, it holds promise in risk stratifying men for biopsy who present with elevated PSA. Herein we report pathologic outcomes in patients treated with radical prostatectomy who had undergone IsoPSA testing prior to their diagnostic biopsy.

Methods:

We conducted a retrospective review of imaging and laboratory results including pathology from patients who had undergone IsoPSA testing prior to biopsy and radical prostatectomy at our institution from 2019-2021. Exploratory analyses were performed to determine whether there is an association between IsoPSA and pathologic features including grade group and incidence of adverse features such as intraductal and cribriform histology, extraprostatic extension, seminal vesicle involvement, surgical margin status, and tumor location on prostatectomy. We also evaluated these data points in a separate randomly selected control group of patients who underwent radical prostatectomy at our institution during the same period but who did not undergo IsoPSA testing as part of their workup. Student’s T-test, Mann Whitney U, and Fisher’s exact test were used where appropriate.

Results:

A total of 83 patients underwent radical prostatectomy following a diagnostic workup that included IsoPSA testing. The mean total PSA was 10.3 ng/dL, IsoPSA index 10.2 (>6 is considered elevated), and prostate size 46.8 gm (Table 1). The incidence of cribriform and intraductal histology on final pathology was 68.7 and 22.9 percent, respectively. There was no difference in IsoPSA index between patients found to have either of these or other adverse features (Table 2). The median IsoPSA index was higher, however, when the dominant tumor was in the transition zone versus the peripheral zone (12.7 vs 8.8, p=0.011). There was no difference in incidence of cribriform and intraductal histology between the IsoPSA and control groups (68.7 vs 68.2% and 22.9 vs 31.8%, respectively).

Conclusion:

IsoPSA has been shown to predict clinically significant disease on biopsy, and as such may improve our ability to select men who would ultimately benefit from such intervention. In this initial set of patients treated with prostatectomy, IsoPSA values were similar between different specific pathologic outcomes except for tumor location, where TZ was associated with increased IsoPSA. Total PSA was similarly elevated in patients with dominant lesions in the TZ. The overall rate of cribriform histology was similar when compared to a control group of patients whom had undergone prostatectomy during the same period for clinically significant disease. IsoPSA reliably identifies patients with clinically significant disease without selecting for unique adverse pathologic features when compared to a control group.

Funding: N/A