Identification of peripheral blood test parameters predicting the response to palbociclib and endocrine therapy for metastatic breast cancer: a retrospective study in a single institution.

Purpose: Cyclin-dependent kinase 4/6 inhibitors have been used in endocrine therapy for patients with estrogen receptor (ER)-positive and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer. Although randomized trials have shown that combined therapies prolong progression-free survival (PFS) in comparison to endocrine monotherapy, the predictors of efficacy are unknown. This study aimed to identify the blood test parameters to predict the effects of palbociclib and endocrine therapy.

Methods: Seventy-nine patients treated with palbociclib and endocrine therapy between December 2017 and June 2022 were reviewed. We assessed PFS in patients according to factors evaluated based on patient characteristics and peripheral blood tests.

Results: Patients in the C-reactive protein (CRP)-high, lactate dehydrogenase (LDH)-high, and albumin (Alb)-low groups had significantly shorter PFS than those in the normal group. A multivariate analysis revealed that high LDH and low Alb levels were independent factors that affected PFS. The Alb-low group had an inferior disease control rate. Patients in the CRP-high, LDH-high, and Alb-low groups who received these therapies as first- or second-line treatments showed poor PFS.

Conclusions: Several predictors of the efficacy of palbociclib and endocrine therapy were identified in the peripheral blood test parameters of patients with ER-positive and HER2-negative subtypes of metastatic breast cancer.