Quantification of skeletal metastases in castrate-resistant prostate cancer predicts progression-free and overall survival

Abstract

Objective: To report a simplified and effective method for substratification of M1 castrate-resistant prostate cancer (CRPC) by correlating progression-free (PFS) and overall survival (OS) with simple quantification of skeletal metastases.

Patients and methods: In all, 561 men with M1 CRPC were studied longitudinally. Individual bone scan disease burden, quantified by counting bone metastasis number, was correlated with clinical outcome using specific threshold points of 1-4, 5-20 and >20 detectable lesions.

Results: Patients with a higher metastasis number had a shorter PFS and OS (hazard ratio [HR] 2.0, 95% confidence interval [CI] 1.7-2.4; P < 0.001). Patients with 1-4 metastases had much better PFS and OS than those with 5-20 metastases. The median PFS and OS in the latter was 10.9 (95% CI 8.4-12.8) and 22.1 (95% CI: 18.5-24.5) months, respectively. PFS and OS for patients with >20 metastases were shorter still [median 5.3 (95% CI 3.4-6.9) months and 13.3 (95% CI 11.3-17.6) months, respectively]. Dichotomising into cohorts with 1-4 and ≥5 metastases, the latter group had considerably poorer PFS [8.4 (95% CI 6.8-10.3) months; P < 0.001) and OS [18.7 (95% CI 17.5-22.1) months; P < 0.001].

Conclusions: Dichotomising patients with CRPC into cohorts with 1-4 or ≥5 skeletal metastases identifies a better and a worse cohort in a manner that is easy and clinically accessible. This simple method facilitates disease stratification and patient management, enabling clinicians to counsel patients more effectively about long-term outcomes and to help select intervention therapies more effectively.

Keywords: CRPC; bone scintigraphy; metastasis; prostate cancer; survival.