Evaluation of Serum Calcium as a Predictor of Biochemical Recurrence following Salvage Radiation Therapy for Prostate Cancer

Table 2

Single variable analysis association between pre-SRT serum calcium and BCR of prostate cancer after SRT.

Serum calcium	Cumulative incidence of BCR (95% CI)			P value
	3 years after SRT	5 years after SRT	RR (95% CI)
Continuous variable (per 0.5 mg/dL increase)	N/A	N/A	0.96 (0.74, 1.25)	0.76
Categorical variable
Low: ≤9.0 mg/dL	41% (26%–54%)	55% (38%–67%)	1.00 (reference)	N/A
Moderate: >9.0 and ≤9.35 mg/dL	40% (26%–52%)	52% (37%–64%)	0.94 (0.59, 1.50)	0.79
High: >9.35 mg/dL	44% (29%–56%)	49% (33%–62%)	1.08 (0.66, 1.75)	0.76

Relative risks, 95% confidence intervals, and P values result from single variable the Cox proportional hazards regression models. BCR: biochemical recurrence. RR: relative risk. CI: confidence interval. SRT: salvage radiation therapy. N/A: not applicable.