ASCO GU 2018: The Perineural Invasion Paradox: Is Perineural Invasion an Independent Prognostic Indicator of Biochemical Recurrence Risk in Patients with pT2N0 Prostate Cancer?

San Francisco, CA ( Perineural invasion (PNI), a pathologic finding on final pathology reports for prostate cancer, either at the time of biopsy or radical prostatectomy, may be a harbinger of worse disease, similar to lymphovascular invasion. It is evident in up to 19% of prostate cancers, per prior reports. Some reports indicate rates up to 84%! However, there is little evidence that PNI is a prognostic factor in patients with localized prostate cancer, specifically as it relates to biochemical recurrence (BCR). Recent series have provided contradictory results.

In this institutional series, the authors from USC examine the role of PNI in their patient cohort. Of 201 men with localized non-metastatic pT2N0 prostate cancer (following RP) between 2008 and 2014, they found that 68.1% (137/201) had perineural invasion and 14% (28/201) had biochemical recurrence. BCR was defined as PSA > 0.2 ng/mL after surgery.

First, they looked at predictors of PNI on final pathology. PNI was associated with pT2c disease, an increased number of positive cores on TRUS biopsy (p < 0.001), and a higher surgical Gleason score (p < 0.001). HAs can be expected, higher volume disease (though not necessarily on final pathology) and higher grade disease was associated with PNI.

On univariate analysis, 19% of patients with PNI had disease recurrence compared to 3.1% without PNI (p = 0.001, Hazard ratio of 6.2). On MVA, accounting for pathologic tumor staging and Gleason score, PNI had a trend towards a significant association with recurrence (p = 0.085, Hazard ratio of 3.2). Obviously, pT2c disease and higher Gleason score were strongly associated with biochemical recurrence.

The authors, in my mind correctly, state that PNI may be an indicator of unfavorable histology rather than an independent prognostic indicator of the risk of biochemical recurrence.

Limitations / Discussion Points:
1. The study is limited by its very narrow patient selection. Patients with pT2N0 disease are at relatively low likelihood of BCR, especially in the time frame analyzed. Hence, the event rate is too low to capture true predictors of BCR.

Presented by: Ryan Kraus, USC Keck School of Medicine Norris Comprehensive Cancer Center, Los Angeles, CA

Written by: Thenappan Chandrasekar, MD, Clinical Fellow, University of Toronto, Twitter: @tchandra_uromd at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA