Breast cancer is the most common cancer in many countries: in Italy about 48.000 new breast cancers are diagnosed every year and, despite improvements in diagnosis and therapy, about 13.000 women die every year for this disease . About 6-7% of breast cancer patients are metastatic at diagnosis , while the majority of patients with stage IV has a previous history of breast cancer that has already been treated. According to various prognostic factors (tumor size, lymph nodes involvement, grading, hormone receptors status, HER-2 status), in the worst-case scenario, more than 30% of node-negative breast cancer patients and more than 70% of node-positive patients relapse2.

The evolution of metastatic breast cancer has changed considerably in the last years with the approval of new drugs. In fact, already in 2003 Giordano et al showed that the prognosis of metastatic breast cancer patients was improved significantly from 1970's to 2000 with a median survival of 15 months in the early 1970's compared with 60 months in the last 1990's.

This significant survival gain was obtained with introduction of new drugs as hormonal, chemotherapeutic and biological agents. The greater availability of drugs has led to an increase in number of lines of treatment receiving by metastatic breast cancer patients. However, there are few published data on actual duration of metastatic breast cancer treatments. Moreover, there is no evidence to support a real impact on survival of treatments beyond the second-third line.

Recently, a retrospective analysis of about 199 metastatic breast cancer patients treated with chemotherapy showed that tumor subtype is associated with the duration and number of lines of chemotherapy (for example HER positive versus "triple-negative" patients) .

The primary objectives are to evaluate the duration of metastatic breast cancer treatments (chemotherapy, hormonal therapy and biological therapies) according to biological subtype (Luminal A, Luminal B, HER2 positive, triple-negative) and to evaluate the number of lines of metastatic breast cancer treatments according to biological subtype (Luminal A, Luminal B, HER2 positive, triple-negative).

The secondary Objectives are to evaluate overall survival according to duration and to number of lines of metastatic breast cancer treatments and to identify predictive factors of number of lines of treatment as for example age, treatment response, biological subtype, metastatic sites, etc and to identify possible elements of different treatment management between participating sites.

The aim of this retrospective and prospective study is to identify the duration of treatments (chemotherapy, hormonal therapy and biological therapies) according to biological subtype and line of treatment in metastatic breast cancer patients.

An ancillary study will be conducted on part of population (HR+/HER2- patients newly diagnosed for mBC receiving first line CDk4/6 inhibitors).

For the ancillary study, it is expected to enroll at least 400 patients, who will be asked to fill in some questionnaires at the following visits, scheduled as per clinical practice:

• PROFFIT: baseline, day 1 cycle 3, day 1 cycle 5, every 6 months thereafter;
• Patient-reported outcomes (PRO): EORTC-QLQ-C30, FACT-B, COST-FACIT at baseline, day 1 cycle 3, day 1 cycle 5, every 6 months thereafter.

The ancillary study could evaluate:

• the impact of first line CDk4/6 inhibitors on HR+/HER2- metastatic breast cancer patients' financial toxicity
• retrospectively, the correlation between NLR and outcome in patients with breast cancer and in treatment with a CDk4/6 Inhibitor (as first line vs as second line)
• the correlation between BMI and outcome in patients with breast cancer and in treatment with a CDk4/6 Inhibitor (as first line vs as second line).

Inclusion Criteria:

Retrospective cohort All consecutive metastatic breast cancers patients treated in the participating site with a first-line therapy (chemotherapy or hormonal therapy with or without biological therapy) from last contact with patient or death which ever event comes first retrospectively back until 1 st of January 2000

Prospective cohort All new consecutive metastatic breast cancers patients will be treated in the participating site with a first-line therapy (chemotherapy or hormonal therapy with or without biological therapy)from site activation to June 2023.

For the ancillary study

• Patients eligible for GIM 14 - BIO-META study
• HR+ HER2- patients newly diagnosed for mBC receiving CDk4/6 inhibitors as first-line or second-line treatment
• Written informed consent

Exclusion Criteria:

Not consecutive metastatic breast cancer patients grouped for a particular biological type (for example: all HER2 positive patients).

Italian patients with metastatic breast cancer