Contemporary validation of cT1a vs. cT1b substaging of incidental prostate cancer

Abstract

Objective: The cT1a vs. cT1b substratification was introduced in 1992 but never formally tested since. We tested the discriminative ability of cT1a vs. cT1b substaging on cancer-specific survival (CSS) in contemporary incidental prostate cancer (PCa) patients.

Design, setting and participants: Incidental (cT1a/cT1b) PCa patients were identified within the Surveillance, Epidemiology, and End Results (SEER) database (2004-2015).

Outcome measurements and statistical analysis: Kaplan-Meier estimates, as well as uni- and multivariable Cox regression models predicted CSS at five years. Subgroup analyses addressed CSS at five years according to active vs. no local treatment (NLT) as well as Gleason score sum (GS; 6 vs. 7 vs. ≥ 8).

Results and limitation: We identified a total of 5,155 incidental prostate cancer patients of which 3,035 (59%) were stage cT1a vs. 2,120 (41%) were stage cT1b. In all incidental PCa patients, CSS at five years was 95% (95% CI 0.94-0.96). In cT1a patients, CSS at five years was 98 vs. 90% in cT1b patients (p < 0.001). In multivariable Cox regression analyses, cT1b independently predicted 2.8-fold higher CSM than cT1a (HR 2.5, 95% CI 1.8-3.6, p < 0.001) for incidental PCa patients who underwent NLT. In subgroup analyses, cT1b represented an independent predictor of higher CSM in GS ≥ 8 (HR 3.0, 95% CI 1.4-6.2, p = 0.003), and GS 7 (HR 3.9, 95% CI 1.6-9.7 p = 0.002) patients who underwent NLT. For actively treated patients, cT1b was not independently associated with worse CSM.

Conclusion: The historical subclassification of cT1a vs. cT1b in incidental PCa patients displayed a strong ability to discriminate CSS in contemporary GS 7 and GS ≥ 8 patients who underwent NLT. However, no statistically significant difference was recorded in actively treated patients. In consequence, the importance of the current substage stratification predominantly applies to GS ≥ 8 patients who undergo a non-active treatment approach.

Keywords: CSS; Incidental prostate cancer; Prognosis; Staging; Validation.