SPINK1 Defines a Molecular Subtype of Prostate Cancer in Men with More Rapid Progression in an at Risk, Natural History Radical Prostatectomy Cohort

Purpose Prostate cancer is clinically and molecularly heterogeneous. We determined the prognosis of men with ERG-ETS fusions and SPINK1 over expression. Materials and Methods Men were identified with intermediate or high risk localized prostate cancer treated with radical prostatectomy and no therapy before metastasis. A case-cohort design sampled a cohort (262) enriched with metastasis from the entire cohort and a cohort (213) enriched with metastasis from patients with biochemical recurrence. We analyzed transcriptomic profiles and subtyped tumors as m-ERG⁺, m-ETS⁺, m-SPINK1⁺ or Triple Negative (m-ERG^─/m-ETS^─/m-SPINK1^─), and multivariable logistic regression analyses, Kaplan-Meier and multivariable Cox models were used to evaluate subtypes as predictors of clinical outcomes. Results Overall 36%, 13%, 11% and 40% of prostate cancer was classified as m-ERG⁺, m-ETS⁺, m-SPINK1⁺ and Triple Negative, respectively. Univariable analysis demonstrated that m-SPINK1⁺ tumors were more common in African-American men (OR 5, 95% CI 1.6–16) but less commonly associated with positive surgical margins (OR 0.16, 95% CI 0.03–0.69) compared to the m-ERG⁺ group. Compared to the Triple Negative group, m-SPINK1⁺ showed similar associations with race and surgical margins in univariable and multivariable analyses across the entire cohort. Survival analyses did not show significant differences among m-ERG⁺, m-ETS⁺ and Triple Negative cases. m-SPINK1⁺ independently predicted prostate cancer specific mortality after metastasis (HR 2.48, 95% CI 0.96–6.4) and biochemical recurrence (HR 3, 95% CI 1.1–8). Conclusions SPINK1 over expression is associated with prostate cancer specific mortality in at risk men with biochemical and clinical recurrence after prostatectomy. ERG-ETS alterations are not prognostic for outcome.