Patients with a history of early breast cancer who develop findings suspicious for metastatic breast cancer should first have a biopsy of one of the suspected metastatic sites to confirm the diagnosis and to assess hormone receptor and HER2 status, as these may differ from the original cancer. A study of suspected metastatic lesions in 121 women with newly metastatic breast cancer showed discordance between the primary and the metastatic site in 16% of specimens for estrogen receptor, 40% for progesterone receptor, and 10% for HER2. Biopsy led to a change in management in 14% of patients. Since bone biopsy specimens cannot be assessed for HER2 status unless there is a soft tissue component, biopsy of an area other than bone is preferred, if possible.

Beginning chemotherapy is inappropriate before the diagnosis of metastatic breast cancer and its hormone receptor and HER2 status are confirmed by biopsy.

Beginning antiestrogen therapy (for example, exemestane combined with everolimus) is also inappropriate before biopsy confirmation of metastatic breast cancer.

Although a PET/CT scan may be useful for staging disease and following response to treatment in patients with metastatic breast cancer, it is important first to establish the diagnosis by biopsy. In this patient, the ultrasound and CT scans have already identified an accessible location for biopsy, and a PET scan is not needed before proceeding to biopsy of one of the liver lesions.