This non-interventional study will collect data from routine diagnostics on HER2 testing of breast cancer in Germany.

Inclusion Criteria:

• Samples derived from men and women of age greater than or equal to (>/=) 18 years
• Samples derived from participants with any stage of histologically confirmed invasive breast cancer with HER2 diagnostics performed within routine (histo-)pathological workup or
• (Histo-)Pathological work-up of the tumor sample as at or after start of this study
• Available information on the year of birth of the participant
• No pre-selection of tumor samples is allowed. Tumor samples have to be documented consecutively in the order of their (histo-)pathological work-up.

Exclusion Criteria:

• Sample derived from participants with any stage of breast cancer with no HER2 diagnostics performed at the time of routine (histo-)pathological work-up.
• Samples derived prior to the start of this study.

Breast cancer tissue samples from participants in Germany