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Exceptional response to cyclophosphamide and dexamethasone in a patient with metastatic castrate-resistant prostate cancer and RB1 mutation.

Rates of prostate cancer relapsing from anti-androgen therapies are increasing in the United States and worldwide. It has been suggested that this is caused by variant and altered lineage marker expression within the tumor, allowing for lineage plasticity that then facilitates therapeutic resistance. The genomic landscape of castrate-resistant prostate cancer has been well-defined with the advent of next-generation sequencing, but the clinical applications of these findings as measured by patient outcomes remains poorly understood. Here, we report on a patient with recurrent, metastatic castrate-resistant prostate cancer and identified RB1 mutation with progressive symptomatology, who was treated with cyclophosphamide and dexamethasone after other standard treatment regimens failed. After completing 2 years of treatment, he experienced complete resolution of his symptoms. Disease remission was confirmed on multiple imaging modalities and through serial measurements of prostate-specific antigen levels that showed a reduction of 99%. Our patient's case supports ongoing research that genetic profiling can help elucidate key biological and molecular tumor components, which can then inform targeted, individualized treatment approaches in the management of recurrent, castrate-resistant prostate cancer.