原文文献：

van Ommen-Nijhof A, Konings IR, van Zeijl CJJ, Uyl-de Groot CA, van der Noort V, Jager A, Sonke GS; SONIA study steering committee. Selecting the optimal position of CDK4/6 inhibitors in hormone receptor-positive advanced breast cancer - the SONIA study: study protocol for a randomized controlled trial. BMC Cancer. 2018 Nov 20;18(1):1146. doi: 10.1186/s12885-018-4978-1.