Non-interventional, multicenter, prospective observational study of tucatinib-trastuzumab capecitabine administered according to the standard local clinical practice following approved SmPC indication and dose.

About 300 Her2 positive metastatic breast cancer patients who are candidate to tucatinib treatment in real world setting including patients previously treated with trastuzumab, pertuzumab, T-DM1, T-DXd as per authorized therapy setting and NPP/EAP ongoing program.

Primary Objective:

To assess the treatment safety and effectiveness as measured by investigator criteria in metastatic breast cancer patients within the real-world setting treated with tucatinib in combination with trastuzumab and capecitabine according to standard local clinical practice following approved Summary of Product Characteristics (SmPC) indication and dose.

The primary purpose of this study is to evaluate the real word effectiveness of the combination therapy "tucatinib/trastuzumab/capecitabine" in mBC patients according to the approved SmPC indication and dose in the real-world setting. Patients with human epidermal growth factor receptor 2 (HER2)- positive metastatic breast cancer who have disease progression after therapy with multiple HER2-targeted agents have limited treatment options. HER2 is a transmembrane tyrosine kinase receptor that mediates cell growth, differentiation, and survival. HER2 is overexpressed in approximately 20% of breast cancers. Both antibody and small-molecule drugs that target HER2 and block its tyrosine kinase activity has been demonstrated to be effective in treating HER2-driven cancers. Tucatinib is an investigational, oral, highly selective inhibitor of the HER2 tyrosine kinase. On April 17, 2020, the Food and Drug Administration approved tucatinib in combination with trastuzumab and capecitabine, for adult patients with advanced unresectable or metastatic HER2- positive breast cancer, including patients with brain metastases, who have received one or more prior anti-HER2-based regimens in the metastatic setting. On 10 December 2020, the European Medicines Agency's (EMA) Committee for Medicinal Products for Human Use (CHMP) adopted a positive opinion, recommending the granting of a marketing authorization for Tukysa (tucatinib) in combination with trastuzumab and capecitabine for the treatment of adult patients with human epidermal growth factor receptor 2 (HER2)-positive locally advanced or metastatic breast cancer (BC) who have received at least two prior anti-HER2 treatment regimens. Tucatinib received a marketing authorization valid throughout the EU on February 2021. The approvals were based on the results of the phase II HER2CLIMB trial in which HER2-positive breast cancer patients, previously treated with trastuzumab, pertuzumab (Perjeta) and trastuzumab emtansine (T-DM1; Kadcyla), have been randomized to receive trastuzumab and capecitabine with either tucatinib or placebo (randomization 2:1).Among the 511 patients with measurable disease at baseline, an objective response was confirmed in 40.6% of patients in the tucatinib-combination group and 22.8% of patients in the placebo-combination group. The primary endpoint of the trial was PFS and the secondary end points comprised overall survival (OS), as well as confirmed objective response rate (ORR). Tucatinib demonstrated efficacy compared with placebo in PFS (7.8 months versus 5.6months) and OS (21.9 months versus 17.4 months). The most common adverse events in the tucatinib arm were diarrhea, palmar-plantar erythrodysesthesia syndrome, fatigue, nausea, and vomiting and transaminitis, even though typically low-grade, transient, and reversible. In addition, out of the ∼600 patients enrolled, 291 patients had brain metastases at baseline. Brain mets including those with active brain mets. Among patients with brain mets PFS at 1 y was 24,9% in the tucatinib combination group vs 0% in the placebo combination group, HR: 0.48;95% CI to 69%;p<0.0001 and median PFS was 7.6 and 5.4 respectively. This represents for many patients the availability of a new valuable therapeutic option especially where the occurrence of brain metastases is frequent. Based on the reported data and considering the clinical benefit of the therapy such as prolongation of PFS/OS, a prospective study on the efficacy and safety profile of the tucatinib in the real-world population can be very useful to follow the evolution of HER2- positive metastatic breast cancer with this promising treatment.

study procedures:

Patients will be managed by their treating clinician without any additional instructions. The study will require no additional treatment procedures during patient visits. Patients meeting the selection criteria will be invited to participate in the study. Before any study-specific data are recorded, patients will be provided with all the study details prior to their decision to participate and will be requested to sign an informed consent form (ICF) prior to their participation in the study. Patient's baseline data, safety, and PS (evaluation according to the Eastern Cooperative Oncology Group [ECOG] score) will be

collected during the observation period (treatment with tucatinib- trastuzumab-capecitabine). Response and survival assessments will

be collected during the study and include symptomatic response and best response by the treating clinician's assessment, according to investigator criteria and the local clinical practice procedures. Safety, response, and survival will be assessed during the follow-up period (18 months post tucatinib treatment). Previous and subsequent non-tucatinib treatments that the patient will receive since the follow-up period will also be described.

Inclusion Criteria:

• Women aged 18 years or older;
• Metastatic breast cancer her2 positive;
• Treatment and treated indication according to local label SmPC and reimbursement for tucatinib-trastuzumab capecitabine treatment;
• At least 2 prior anti her2 treatment in any setting;
• Written informed consent indicating that patients understand the purpose and procedures and are willing to participate in the study.

Exclusion Criteria:

• Patients with diseases or significant clinical condition, according to the findings of the investigator, may interfere with the study evaluations;
• Absence of any radiological assessment;
• No data on tucatinib efficacy and safety.

Her2 positive metastatic breast cancer patients who are candidate to tucatinib treatment in real world setting including patients previously treated with trastuzumab, pertuzumab, T-DM1, T-DXd as per authorized therapy setting and NPP/EAP ongoing program.