CDK4/6 inhibitors beyond second line, is it worthy? A real-world data experience.

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e13033 Background: CDK4/6 inhibitors as Palbociclib, Ribociclib and Abemaciclib has become the first or second line in advanced or metastatic luminal breast cancer HER2 negative. We only have data about the use of Abemaciclib in monotherapy beyond second line. Methods: We have analyzed 200 patients treated in our center with CDK4/6 inhibitors since 2017. All of them belong to clinical practice, out of clinical trial context. The effect of CDK4/6 inhibitors was analyzed using logistic regression analyses. Results: 34 patients were treated beyond second line of treatment with a medium follow-up of 18 months. CDK4/6 inhibitors were used as fourth line as medium (range 3-9), median age of 45 years, 1 male. 52% patients had visceral disease and 8.8% were primary hormone resistance. 64.6% were treated with palbociclib, 26.5% with ribociclib and 8.8% with abemaciclib. 52.9% were asociated with Fulvestrant, 44.1% with Letrozol and 2.9% with tamoxifen. Clinical benefit of 67.6% and response rate of 32.3%. Similar toxicities to previosly published trials were observed. Median progression-free survival was 14.2 months and median overal survival was 26.6 months. Non statistical difference were observed by luminal subtype, number of prior lines, type of hormonal therapy or CDK4/6 inhibitor used. Conclusions: Despite of the small population, we can summarized that CDK4/6 inhibitors associated to hormonal therapy is a good option for patients previosly treated in the metastatic setting. We need further investigation to understand which patient will benefit from treatment with this drugs in advanced lines.

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