IntroductionAs multigene panel testing (MGPT) is increasingly incorporated into clinical oncology [1], a clear understanding of its psychological impact on test recipients is essential. Prior studies indicate that relatives generally report lower levels of distress than probands [2], that cancer worry decrease among unaffected relatives following cascade testing [3], and that distress often rises immediately after result disclosure before decline over time [4]. Such psychological responses can influence screening behaviors [5] and quality of life [6]. The psychological effects of genetic testing are commonly measured using instruments such as the Cancer Worry Scale (CWS) [3, 7, 8], the Impact of Event Scale (IES) [2, 4], and the Multidimensional Impact of Cancer Risk Assessment (MICRA) [9,10,11].Although clinical uptake of MGPT varies by country [12,13,14,15], its use in affected probands is widespread, and in recent years, its application to cascade testing for relatives has been increasingly explored [16, 17]. Existing research on relatives has largely focused on those identified as carriers of germline pathogenic variants (GPVs) [2] or on single-site testing approaches [2, 3]. Moreover, most MGPT-related psychological research has targeted affected probands [7, 10, 11], leaving the psychological impact of cascade testing using MGPT on unaffected first-degree relatives insufficiently characterized.This study aims to clarify the psychological impact of cascade testing using MGPT on unaffected relatives of individuals with hereditary cancer. Specifically, it seeks to (1) assess the extent of genetic test–related distress following cascade testing using MGPT and examine its associations with demographic and clinical factors; (2) evaluate changes in cancer worry before and after the disclosure of test results; and (3) compare cancer worry between unaffected relatives and individuals with cancer at both pre- and post-disclosure time points.MethodsStudy design and participantsThis psychological sub-study was conducted as part of the BRANCH study (UMIN000046085), which aimed to evaluate the clinical utility of MGPT in Japanese oncology practice among individuals with cancer and their first-degree relatives diagnosed with hereditary cancer.Between June 2022 and October 2023, 49 institutions participated in the BRANCH study. As of October 2023, the BRANCH study comprised four cohorts (Supplementary Fig. 1). The eligibility criteria for participants included being ≥20 years of age between June and August 2022 and ≥18 years of age from September 2022 onward. The participants were required to be proficient in reading, writing, and speaking Japanese. The study protocol was approved by the Institutional Review Board of the National Cancer Center (2021-194) and the ethics committees of all participating institutions.In this sub-study, we defined unaffected relatives as cancer-unaffected first-degree relatives of cancer-affected probands in whom GPVs were identified in pre-specified genes (Supplementary Table 2a). These unaffected relatives were derived from Cohort C of the BRANCH study. To assess the differences in cancer worry according to cancer history, individuals with cancer were defined as the control group. Individuals with cancer were derived from a subset of Cohort C and from Cohort D. In Japan, the majority of genetic tests for hereditary cancer are not covered by public health insurance. However, BRCA1 and BRCA2 testing (BRCA1/2 testing) (Myriad Genetics, Salt Lake City, UT, USA) is covered by public insurance for individuals who meet specific clinical criteria. Individuals with cancer who fulfilled at least one of these criteria were included in the study. (1) individuals with cancer who had previously undergone BRCA1/2 testing and received the results (Cohort D), or (2) first-degree relatives of patients with hereditary cancer with a personal history of cancer (a subset of Cohort C) (Supplementary Fig. 2).Study proceduresThe study flow is presented in Supplementary Fig. 1. During the informed consent process, participants were given the option to receive either information limited to the proband’s variant or the full results of MGPT. Electronic informed consent was obtained from all participants, after which peripheral blood samples were collected. MGPT targeted 35 genes associated with hereditary cancer syndromes (Supplementary Table 2b). This MGPT includes hereditary tumor predisposition genes associated with increased risks of breast, ovarian, colorectal, and pancreatic cancer. Testing was conducted by FALCO Biosystems (Kyoto, Japan) and included the detection of single-nucleotide variants, insertions/deletions, and copy number variations. For unaffected relatives, single-site analysis was performed using Sanger sequencing or multiplex ligation-dependent probe amplification (MLPA) to identify known proband-specific pathogenic variants. Genetic testing results were classified according to the American College of Medical Genetics and Genomics guidelines [18], as follows:(i) Pathogenic or likely pathogenic variant (GPV)(ii) Variant of uncertain significance (VUS)(iii) Negative (benign or likely benign)Ten days after blood collection, participants completed the first electronic patient-reported outcome (ePRO) questionnaire (T0). At T0, participants responded to items assessing their demographic characteristics (marital status, presence of children, education level, and income), clinical information (personal and family history of cancer and current screening status) and Japanese version of the Cancer Worry Scale (CWS-J) (Supplementary Table 1).The genetic testing results were returned to each institution. Based on each participant’s preference for the scope of disclosure, results were disclosed by the attending physician. Those who opted for MGPT disclosure received the results for all 35 genes, including VUS.Two weeks after disclosure, participants completed the second ePRO (T1). At T1, they responded to the CWS-J, the revised Impact of Event Scale (IES-R), and additional questions regarding family discussions about cancer risk and satisfaction with the genetic testing experience (Supplementary Table 1).Only participants who completed both T0 and T1 assessments were included in the analysis. Demographic and clinical data (sex, age, ethnicity, recurrence, metastasis) were collected using an electronic data capture system (Supplementary Table 1). Genetic test results were provided by FALCO Biosystems. Participants were categorized into three groups: GPV group (with or without coexisting VUS), VUS group (VUS only), and negative group (neither GPV nor VUS).Psychological assessment toolsThe CWS is an eight-item questionnaire that assesses anxiety regarding cancer risk and its impact on daily life. Items were rated on a 4-point scale, and scores ≥14 were defined as high cancer worry (CWS-high) [19] (Supplementary Table 3). In this study, scores ≥14 and