Molecular and clinical characterization of KLK2 mRNA expression in prostate cancer (PC).

5050 Background: KLK2 is an androgen-regulated gene that plays a critical role in PC biology. Given the development of KLK-2 targeted therapies, we sought to characterize the molecular and clinical features associated with KLK2 mRNA expression in PC. Methods: NextGen sequencing of DNA (592-gene/whole exome) and RNA (whole transcriptome) was performed on PC specimens (n=6,978) at Caris Life Sciences. KLK2-High/Low expression was defined as >75 th /<25 th quartile RNA transcripts per million (TPM). Castrate resistant PC (CRPC) and hormone sensitive PC (HSPC) were defined based on androgen deprivation therapy (ADT) duration prior to tissue collection: HSPC < 3 and CRPC ≥ 3 months from ADT start. Overall survival (OS) was defined as the time of collection or first androgen receptor pathway inhibitor (ARPI) to death/last follow-up. Results: Specimens were derived from primary prostate (n=4,464, 64.0%), lymph nodes (n=828, 11.9%) or other metastatic sites (n=1,686, 24.2%). Higher KLK2 was observed in tumors from Black vs. White patients (8.88 vs. 8.75 log 2 [TPM+1], p<0.001). KLK2 was enriched in adenocarcinoma vs. mixed vs. NEPC (8.79 vs. 7.58 vs. 0.33 log 2 [TPM+1], p<0.001). Relative to primary tumors (8.93 log 2 [TPM+1]), KLK2 varied by metastatic site, with lowest expression in GI (7.46 Log 2 [TPM+1], p<0.001), liver (7.88 log 2 [TPM+1], p<0.001), and CNS (8.25 log 2 [TPM+1], p<0.001). In primary tumors, high KLK2 associated positively with SPOP and negatively with PI3K/PTEN , TP53 , and RB1 alterations. Across primary, lymph node, and distant metastatic tumors, high KLK2 associated positively with AR signaling and negatively with NEPC signaling (all p<0.001). KLK2 strongly correlated with KLK3 (PSA) expression (R=0.87). KLK2 expression was higher in HSPC (n=1504) vs. CRPC (n=4519) tumors (1.78 Log 2 [TPM+1], p<0.001). Among HSPC, KLK2-high tumors had decreased TP53 , RB1 , AKT1 , BRCA1 and increased SPOP , CTNNB1 , PTEN , BRCA2 mutations. CRPC tumors with high KLK2 had decreased RB1 , TP53 , PIK3CA and increased RAD54L and ATM mutations compared to low tumors. High KLK2 was associated with improved OS from collection time (median 69.7 vs. 35.9 months, p<0.001) and first ARPI initiation (median 48.9 vs. 39.5 months, p<0.001). KLK2-high HSPC and CRPC tumors had improved OS compared to low tumors (median 82.0 HSPC KLK2-high vs. 54.3 HSPC KLK2-low vs. 23.7 CRPC KLK2-high vs. 16.3 CRPC KLK2-low months, q<0.01). The combination of KLK2-high/AR-high was associated with increased OS compared to KLK2-high/AR-low, KLK2-low/AR-high, and KLK2-low/AR-low tumors (median 70.8 vs. 48.8 vs. 43.5 vs. 20.8 months, respectively, p<0.001). Conclusions: This large-scale clinic-genomic analysis reveals distinct patterns of KLK2 expression in PC. The correlation between high KLK2 expression, favorable genomic features, and improved OS supports its potential utility as a prognostic biomarker and may inform selection for KLK2-directed therapy.