The treatment options for cancer of unknown primary (CUP) are challenging due to the lack of knowledge about the primary sites, often resulting in a poor prognosis. The emerging next-generation sequencing (NGS) technique has provided a reliable approach to facilitate tumor primary site prediction and targetable gene alteration identification for CUP patients. In this report, we described a 63-year-old female patient who experienced recurrent CUP. NGS-based genetic profiling results revealed a pathogenic germline BRCA1 R71K mutation. Accordingly, the patient received the poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitor olaparib treatment and demonstrated a favorable response to this treatment. Our case suggests that NGS holds great promise for providing improved diagnosis and treatment options to patients with CUP, warranting further clinical investigation.