Precision medicine is rapidly changing the diagnostic and treatment spectrum of oncology. In May 2019, comprehensive genomic profiling (CGP) (somatic and/or germline) was approved for reimbursement in Japan. While the promise of novel and targeted therapies has elevated hopes for the benefits of CGP, the lack of relevant genomic findings and/or limited access to relevant therapies remain important themes in this field. These challenges may also negatively influence the psychology of both cancer patients and their family members. However, few studies have reported longitudinal data on quality of life (QOL) with CGP. Here, we report the protocol of a prospective study, Q-CAT (QOL for Cancer genomics and Advanced Therapeutics among patients and their family members), which aims to explore the mental burden on patients and families arising from the implementation of CGP testing by collecting real-world longitudinal data using outcomes obtained with an electronic patient report, known as ePRO. This study has been registered with the Japan Registry of Clinical Trials (jRCT1030200039).