The prognosis of patients with progressive prostate cancers that are hormone refractory and/or have bone metastasis is poor. Therefore, multiple therapeutic targets to improve prostate cancer patient survival have been investigated. In this study, we identified 7 genes as a candidate therapeutic molecule using integrative gene expression analyses of registered Big Data sets for prostate cancer cell lines and prostate cancers of the patients with or without bone metastasis. Among them, we focused on G Protein-Coupled Receptor Class C Group 5 Member A (GPRC5A) because of its highest expression level in bone metastatic cells. Kaplan-Meier analysis of TCGA data sets revealed that patients who have high GPRC5A expression had significantly shorter overall survival. PC3 prostate cancer cells with CRISPR/Cas9-mediated GPRC5A knockout exhibited significantly reduced cell proliferation both in vitro and in vivo. RNA-seq revealed that GPRC5AKO PC3 cells had dysregulated expression of cell cycle-related genes, leading to cell cycle arrest at the G2/M phase. Furthermore, the registered gene expression profile data set showed that the expression level of GPRC5A in original lesions of prostate cancer patients with bone metastasis was higher than that without bone metastasis. In fact, GPRC5AKO PC3 cells failed to establish bone metastasis in xenograft mice models. In addition, our clinical study revealed that GPRC5A expression levels in prostate cancer patient samples were significantly correlated with bone metastasis as well as the patient's Gleason score (GS). Combined assessment with the immunoreactivity of GPRC5A and GS displayed higher specificity for predicting the occurrence of bone metastasis. Together, our findings indicate that GPRC5A can be a possible therapeutic target and prognostic marker molecule for progressive prostate cancer.