A Study to Measure the Expression of the HER2-HER3 Dimer in Tumour and Blood (Exosomes) Samples From Patients With HER2 Positive Breast Cancer Receiving HER2 Targeted Therapies

The study will recruit 40 participants to two groups as outlined below: Group 1: Early HER2 positive breast cancer (20 patients) Group 2: Metastatic HER2 positive breast cancer (20 patients) The two groups represent the natural spectrum of breast cancer in its clinical presentation. GROUP 1: EARLY BREAST CANCER Group 1 will include patients with early HER2 positive breast cancer recommended to receive neo-adjuvant chemotherapy inclusive of HER2 directed therapy (trastuzumab + pertuzumab), prior to proceeding to curative surgery. All participants are expected to have had a diagnostic core biopsy and definitive breast surgery on completion of neoadjuvant chemotherapy as standard of care. Blood samples will be obtained for biomarker analysis in exosomes. Participants in Group 1 A will be requested to have a biopsy on completion of anthracycline based chemotherapy and prior to commencing on HER2-directed therapy. Group 1 A: Participants in Group 1 commencing treatment with anthracycline based chemotherapy for up to 4 cycles followed by a switch in treatment to taxane based chemotherapy in combination with HER2 directed therapy (trastuzumab + pertuzumab) for up to 4 cycles Group 1 B: Participants in Group 1 commencing treatment with taxane based systemic therapy in combination with HER2 directed therapy (trastuzumab + pertuzumab) for up to 6 cycles: GROUP 2: METASTATIC BREAST CANCER: Group 2 will include patients will include participants recommended commencing any line of palliative systemic therapy inclusive of a HER2 directed therapy by their treating oncologist. All participants are expected to have had a diagnostic core biopsy. Blood samples will be obtained for biomarker analysis in exosomes.