• 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

• 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

• 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