Palbociclib and letrozole in hormone-receptor positive advanced breast cancer: Predictive response and prognostic factors

CDK 4/6 inhibitors have been yielding propitious results when with hormone therapy in the management of Her2-negative and hormone-receptor (HR)-positive metastatic breast cancer, palbociclib being one of the first molecules investigated in this setting. However, the response to CDK4/6 inhibitors is variable. To identify predictive and prognostic factors of response to this therapeutic regimen. Eligible patients were females with HR+ and Her2- advanced breast cancer, receiving Palbociclib in combination with Letrozole. PFS was the primary endpoint in the evaluation of response to treatment. This survival was then further segregated according to various characteristics: histological (type, grade, hormone receptors), metastatic site, line of treatment, response type at initial assessment, and best response achieved. The data was then processed by two statistical analysis models: Kaplan-Meier and univariate preceding multivariate Cox proportional risks. Sixty patients were included and followed for a median follow-up duration of 15.98 months. PFS recorded a median of 19.07 months (95% CI=15.43-22.71). PFS had a median of 12.99 months in the absence of progesterone receptors (vs 20.05 months in the case of positive estrogen and progesterone receptors; P = 0.046), a median of 13.02 months in the presence of liver metastases (vs 22.98 months in the absence of liver metastases; P = 0.007), and 15.94 months in the case of second-line and beyond (vs 22.98 months in the case of first-line; P = 0.033). Regarding the Hazard Ratio of progression, we note age (HR 0.941; P = 0.019), liver metastases (HR 2.751; P = 0.051), response at initial evaluation (HR<1; P < 0.001) and best response (HR<1; P = 0.003). PFS reached similar figures to those of international studies. The absence of progesterone receptors, presence of liver metastases, and use as second-line or beyond are associated with a reduced median PFS. One year age increase (protective factor), liver metastases (risk factor), response at initial evaluation, and best response achieved are identified as the most predictive factors of the response to this treatment regimen and of the progression risk.