Miwa, TakeshiTakeshiMiwaStrong, CarolCarolStrongKu, Stephane Wen-WeiStephane Wen-WeiKuLi, Chia-WenChia-WenLiPOYAO HUANGWu, Huei-JiuanHuei-JiuanWuYamaguchi, MasazumiMasazumiYamaguchiIkushima, YuzuruYuzuruIkushima2026-01-302026-01-302026-01https://scholars.lib.ntu.edu.tw/handle/123456789/735684To understand opportunities for improving pre-exposure prophylaxis (PrEP) uptake, this study constructed a PrEP cascade and examined subgroup profiles associated with transitions along the cascade among gay, bisexual, and other men who have sex with men (gbMSM) in Japan. An online cross-sectional survey was conducted from February to March 2021. The four-step PrEP cascade included awareness, willingness, initiation, and regimen use. Latent class analysis (LCA) identified participant subgroups, and logistic regression examined associations with the most significant drop-off in the cascade. Among 5,831 cisgender gbMSM not living with HIV (median age: 38 years), 52.6% were aware of PrEP, 76.4% of whom were willing to use it. However, only 20.5% of those willing had initiated PrEP-the largest decline in the cascade. Among those who initiated, 43.8% were on a daily regimen. LCA identified four subgroups: (i) Sexual Adventurers (32.1%)-high sexual activity and strong HIV community ties; (ii) Reserved Bystanders (26.7%)-low engagement with the HIV community and sexual health services; (iii) Positive Allies (24.6%)-strong HIV community ties and comfort discussing sexual health; and (iv) Young Explorers (16.7%)-younger, moderately sexually active, with limited HIV community ties. Compared to Reserved Bystanders, Sexual Adventurers (OR 5.27, 95% CI 3.91-7.10) and Positive Allies (OR 1.60, 95% CI 1.14-2.26) had significantly higher odds of PrEP initiation. Despite increasing acceptability, barriers to PrEP uptake persist. Targeted interventions are needed to address subgroup-specific challenges-particularly for younger gbMSM and those with limited access to HIV community networks and sexual health services.enCascadeCross-sectional surveyJapanLatent class analysisMen who have sex with menPre-exposure prophylaxisjournal article10.1007/s10461-025-04854-040810881