Table 4.

Risk for development of first on-treatment SSE.

Characteristic	Risk for SSE Development
	HR	95% CI	p-Value
Univariate analysis
Metastatic compartment
Bone-only Bone + extra-bone metastases	Reference 1.40	Reference 1.14–1.72	0.002
Age (years)
≤50 >50 to ≤65 >65 to ≤75 >75	Reference 0.53 0.38 0.34	Reference 0.27–1.03 0.19–0.73 0.17–0.68	0.063 0.004 0.002
ECOG performance status
≤1 2	Reference 1.39	Reference 0.99–1.95	0.055
Gleason score
≤6 7 ≥8	Reference 0.92 1.27	Reference 0.72–1.19 1.01–1.62	1.188 1.619
PSA at disease diagnosis, ng/mL
<10 ≥10	Reference 1.29	Reference 1.02–1.63	0.031
Type of bone metastases
Lytic Blastic Mixed	Reference 0.99 0.90	Reference 0.63–1.55 0.55–1.48	0.952 0.672
Number of bone metastases
≤2 >2	Reference 1.07	Reference 0.89–1.28	0.454
Previous SREs
No Yes	Reference 1.63	Reference 1.35–1.96	<0.001
Castration type
Chemical Surgical Both	Reference 0.37 0.67	Reference 0.21–0.64 0.54–0.82	<0.001 <0.001
Currently receiving chemotherapy
No Yes	Reference 1.47	Reference 1.17–1.84	0.001
Previous chemotherapy
No Yes	Reference 1.32	Reference 1.09–1.60	0.004
Previous radiotherapy
No Yes	Reference 1.48	Reference 1.24–1.76	<0.001
Previous antineoplastic surgery (any)
No Yes	Reference 0.93	Reference 0.79–1.11	0.439
Multivariate model; n = 1901
Covariates: Age, ECOG PS, Gleason score, PSA at diagnosis, number of bone lesions, previous SREs, castration type, and previous surgery and radiotherapy
Metastatic compartment
Bone-only Bone + extraskeletal metastases	Reference 1.30	Reference 1.06–1.61	0.014

CI, confidence interval; ECOG PS, Eastern Cooperative Oncology Group performance status; HR, hazard ratio; PSA, prostate-specific antigen; SRE, skeletal-related event; SSE, symptomatic skeletal event.