Elacestrant in Patients With ER+ HER2- ESR1-mutated Locally Advanced or Metastatic Breast Cancer

Elacestrant in Patients With ER+ HER2- ESR1-mutated Locally Advanced or Metastatic Breast Cancer: a Multicenter, National, Prospective Non-interventional Study

The objective of this non-interventional study (NIS) is to evaluate prevalence of ESR1 mutation after endocrine therapy in the palliative setting, quality of life, tolerability, and safety and to describe treatment detail and adverse event (AE) management in postmenopausal women with locally advanced and/or metastatic ER+ HER2- ESR1-mutated breast cancer and second line treatment with elacestrant according to SmPC (Summary of product characteristics) in a real-world setting.

Inclusion Criteria:

• Signed and dated informed consent form
• Postmenopausal women
• Age ≥18 years
• Eastern Cooperative Oncology Group Performance Status (ECOG) < 2
• Locally advanced and/or metastatic ER+ HER2- breast cancer
• Histologically proven ER positivity (defined as ≥1% staining by immunohistochemistry (IHC))
• Histologically proven HER2 negativity (defined as a IHC0 or IHC1+ score by IHC or a negative result by in situ hybridization (ISH), optionally combined with a IHC2+ score)
• Disease progression following first line ET + CDKi
• No more than one prior ET line in the advanced/metastatic setting and intention for 2nd-line treatment with elacestrant according to current elacestrant SmPC as assessed by the treating physician (ESR1 testing can be done after inclusion)
• For patients with proven ESR1mut: Study inclusion the latest 2 weeks after start of elacestrant treatment

Exclusion Criteria

• Prior chemotherapy in the advanced/metastatic setting
• Contraindications according to elacestrant SmPC, except for ESR1 test result for patients included prior to ESR1 testing.
• Participation in an interventional clinical trial within 30 days prior to enrolment or simultaneous participation in an interventional clinical trial (except follow-up phase)