Background. Previous reports have shown a positive association between serum calcium level and prostate cancer mortality. However, there is no data regarding whether higher serum calcium levels are associated with increased risk of biochemical recurrence (BCR) following salvage radiation therapy (SRT) for prostate cancer. Herein, we evaluate the association between pretreatment serum calcium levels and BCR in a cohort of men who underwent SRT. Methods. We evaluated 165 patients who underwent SRT at our institution. Median dose was 65.0？Gy (range: 54.0–72.4？Gy). We considered serum calcium as both a continuous variable and a 3-level categorical variable (low [≤9.0？mg/dL], moderate [>9.0？mg/dL and ≤9.35？mg/dL], and high [>9.35？mg/dL]) based on sample tertiles. Results. We observed no evidence of a linear association between serum calcium and BCR (relative risk (RR): 0.96, ). Compared to men with low calcium, there was no significantly increased risk of BCR for men with moderate (RR: 0.94, ) or high (RR: 1.08, ) serum calcium levels. Adjustment for clinical, pathological, and SRT characteristics in multivariable analyses did not alter these findings. Conclusion. Our results provide evidence that pretreatment serum calcium is unlikely to be a useful tool in predicting BCR risk following SRT. 1. Introduction Approximately, one-third of men treated with a radical prostatectomy (RP) for prostate cancer will have biochemical recurrence (BCR) within 10 years, and in two-thirds of these men on active surveillance, metastatic disease develops within 10 years [1]. Salvage external beam radiation therapy (SRT) appears to positively affect this natural history when it is initiated early in the course of postoperative BCR [2–4]. A key clinical issue centers on the need to predict which patients with a detectable serum prostate-specific antigen (PSA) after RP have local recurrence versus micrometastatic disease. Accurate means of distinguishing these two groups of men would allow for better selection of patients as candidates for local SRT. We developed and published a scoring algorithm based on readily available clinicopathologic features to help predict which men will experience BCR after SRT and thus provide a guide for clinicians when counseling patients [2]. More recently, we evaluated RP specimens for the ability of specific tumor-based biomarkers (e.g., Ki-67 and B7-H3) to predict which men will respond to SRT [5–7]. Based on our reports, information on clinicopathologic features and tumor-based biomarkers can assist in the appropriate selection of men as good
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