Metastasis to the brain occurs in a significant fraction of patients with breast cancer (1-3). We mined published RNA-sequencing and microarray data (4, 5) to compare primary and metastatic tumor transcriptomes for the discovery of genes associated with brain metastasis in humans with metastatic breast cancer. We found that pyrroline-5-carboxylate reductase 1, encoded by PYCR1, was among the genes whose expression was most different in the brain metastases of patients with metastatic breast cancer as compared to primary tumors of the breast. PYCR1 mRNA was present at increased quantities in brain metastatic tissues as compared to primary tumors of the breast. Expression of PYCR1 in primary tumors was correlated with patient overall, distant metastasis-free and recurrence-free survival. Modulation of PYCR1 expression may be relevant to the biology by which tumor cells metastasize from the breast to the brain in humans with metastatic breast cancer.