Objective To investigate the correlation between preoperative systemic immune-inflammation index (SII), plasma fibrinogen to albumin ratio (FAR) and bone metastasisin in patients with prostate cancer.

Methods The clinical data of 118 patients with prostate cancer was retrospectively reviewed, and the patients included 40 cases with bone metastasis and 78 cases without bone metastasis.

Results The SII and FAR values in patients with bone metastasis were higher than those in patients without bone metastasis (P ＜ 0.01). The results of multivariate logistic regression analysis showed that for each increase of one unit in SII and FAR (standardized), the probability of metastasis was 1.003 times and 6.604 times that of non- metastasis, respectively. The area under the ROC curve (AUC) of SII for diagnosing bone metastasis of prostate cancer was 0.799 (95%CI: 0.713–0.885), the optimal cut-off value was 406.917, the sensitivity was 87.5%, the specificity was 67.9%, and the Youden index was 0.554. The AUC of FAR in diagnosing bone metastasis of prostate cancer was 0.853 (95%CI: 0.769–0.937), the optimal cut-off value was 0.101, the sensitivity was 67.5%, the specificity was 98.7%, and the Youden index was 0.662. The AUC of SII combined with FAR for predicting bone metastasis of prostate cancer was 0.873 (95%CI: 0.796–0.950), the optimal cut-off value was 0.558, the sensitivity was 70.0%, the specificity was 98.7%, and the Youden index was 0.687.

Conclusions The values of SII and FAR are correlated with newly diagnosed prostate cancer patients who have already developed bone metastasis. The efficacy of combined detection of SII and FAR in the correlation of bone metastasis in newly diagnosed prostate cancer patients is higher than that of separate detection of the two indicators, which is more conducive to the risk prediction of bone metastasis in newly diagnosed prostate cancer patients.