Phase II Single-Arm Two-Stage Designs with Time-to-Event Outcomes R package OneArm2stage version 1.2.1 Two-stage design for single-arm phase II trials with time-to-event endpoints (e.g., clinical trials on immunotherapies among cancer patients) can be calculated using this package. Two notable advantages of the package: 1) It provides flexible choices from three design methods (optimal, minmax, and admissible), and 2) the power of the design is more accurately calculated using the exact variance in the one-sample log-rank test. The package can be used for 1) planning the sample sizes and other design parameters, and 2) conducting the interim and final analyses for the Go/No-go decisions. More details about the design method can be found in: Wu, J, Chen L, Wei J, Weiss H, Chauhan A. (2020). <doi:10.1002/pst.1983>. Software Depends: R (>= 3.5.0) Imports: survival, utils, flexsurv, IPDfromKM Suggests: knitr, rmarkdown, testthat (>= 3.0.0) Xiaomeng Yuan <xiaomeng.yuan@stjude.org> Comprehensive R Archive Network (CRAN) Xiaomeng Yuan [aut, cre], Haitao Pan [aut], Jianrong Wu [aut] GPL (>= 3) 2023-10-09 application/tgz https://CRAN.R-project.org/package=OneArm2stage doi:10.32614/CRAN.package.OneArm2stage