PALMARES-2 is a retrospective/prospective, observational, multicenter, population-based study, aiming at providing real-world evidences on HR+/HER2- aBC patients treated with first-line CDK4/6i plus ET. The present study has the objective to collect data coming from different sources, i.e. RWD, medical images and biological samples, from patients treated with CDK4/6i as first-line of therapy for HR+/HER2- aBC. In consideration of the complexity of data collected and different objectives of the study, this master protocol foresees different sub-studies, which encompasses different methodologies for data collection, data extraction and analyses.

The PALMARES-2 study aims to collect data from different sources, i.e. real-world clinical data, medical images and biological data and samples, from patients treated with CDK4/6i as first-line therapy for patients with HR+/HER2- advanced breast cancer. Due to the complexity of the data collected and the different objectives of the study, this protocol includes several sub-studies, which include different methodologies for data collection, extraction and analysis:

• The first sub-study (RWD sub-study) will aim to collect real-world clinical data of patients who received ET+CDK4/6i in the first-line setting; the primary objective of this sub-study is to assess whether there is a difference in OS between the three CDK4/6i in the real-world population, while secondary objectives include comparisons in specific sub-groups;
• The second sub-study (Safety sub-study) includes the collection of comorbidities, concomitant medications and toxicities of patients enrolled in the study; the primary objective of this sub-study is to evaluate the difference in severe toxicity between the three CDK4/6i in the real-world population
• The third sub-study (medical imaging sub-study) consists of the collection of computed tomography (CT) and fluorodeoxyglucose positron emission tomography (FdG-PET) images at baseline and digitised haematoxylin-eosin (HE) slides to build a multi-omics predictive model;
• The fourth sub-study (translational sub-study) aims to collect tumour samples from a proportion of patients enrolled in the study to perform genomics and transcriptomics analyses; information from this data source will be integrated into the model built with the previous data to further improve the performance of the previous model
• The fifth sub-study (subsequent lines sub-study) focuses on the lines of treatment administered to patients enrolled in the study at the time of progression after first-line treatment with ET+CDK4/6i, with the aim of building predictive models of response to subsequent lines of treatment, capable of supporting oncologists' and patients' decisions in this context.

Inclusion Criteria:

• Diagnosis of HR+/HER2- advanced Breast Cancer (aBC), as defined as at least 1% estrogen receptor (ER) and/or progesterone receptor (PgR) positivity at IHC. HER2 negativity is defined on the basis of an IHC score of 0, 1+, or 2+ with absence of gene amplification at in situ hybridization (ISH) analyses.
• Have received or are candidate to receive treatment with palbociclib, ribociclib or abemaciclib in combination with endocrine therapy as first-line treatment for HR+/HER2- aBC.

Exclusion Criteria:

• Less than 3 months of follow up from the CDK4/6i start to the date of data cut-off;
• Have received CDK4/6i as monotherapy;
• Have received CDK4/6i as adjuvant treatment for localized disease.

The study involves the retrospective and prospective collection of consecutive HR+/HER2- advanced Breast Cancer patients (defined as metastatic or locally advanced not candidate for definitive curative intervention) treated with CDK4/6i in combination with endocrine therapy as first-line treatment for advanced disease in different Italian cancer centers.

IPD will be evaluated for submission