A Study to Investigate Mechanisms of Resistance to Breast Cancer Therapies

This study will evaluate mechanisms of resistance to anti-breast cancer therapies in tumor and blood samples from participants with human epidermal growth factor receptor (HER2) positive, hormone receptor (HR) positive or triple negative breast cancer.

• General Inclusion Criteria: * Willingness to undergo a procedure to obtain tumor tissue (e.g. biopsy) and blood draw * Diagnosis of HER2+, HR+ (for cohort R1) or triple negative breast cancer (for cohort T1) as per local assessment * Availability of an archival tumor tissue (most recent pre-treatment tumor tissue is preferred) * Unequivocally growing tumor lesion (progressive lesion) that is accessible for resection, excision or core needle biopsy * Discontinuation of prior anti-cancer treatment outlined below should not be longer than 4 weeks from participation in this study Inclusion criteria for participants in the cohorts studying acquired resistance * Participant had undergone regular monitoring for disease progression as per local practice (preferably every 3-6 months) while on most recent breast cancer therapy * Accessible tumor lesion that newly appeared or a lesion that started to regrow while the participant was at least 6 months on therapy Inclusion criteria for participants in the cohort studying primary resistance * Accessible tumor lesion that continued to increase in size or a newly appearing lesion (as confirmed by routine tumor assessment) while treated for at least 4 weeks but less than 6 months on therapy

Use the source registry for the full inclusion and exclusion criteria before discussing referral or enrolment.