Molecular Mechanisms of Resistance and Sensitivity to Palbociclib Re-challenge in ER+ mBC

This is an international, open-label, non-controlled, multicenter phase II clinical trial with two different primary objectives: a biological and a clinical objective. From a clinical point of view, the objective is to assess the clinical benefit of the combination of palbociclib and hormonotherapy in patients with advance breast cancer that had previously received endocrine therapy in combination with palbociclib and had achieved clinical benefit during palbociclib treatment with subsequent disease progression. From a biological point of view, the challenge is to define a molecular profile that allow identifying patients that could benefit more from continuing on palbociclib after progression on a prior palbociclib-containing regimen