Case 1: Bonnie (58 years old)

Bonnie, 58 years old, was diagnosed with primary metastatic breast cancer 16 months ago.

Assessment summary:

• Postmenopausal
• No family history of breast cancer
• No relevant medical history, ECOG PS: 0
• Diagnosed with primary metastatic breast cancer 16 months ago
• Imaging:
  • 5 cm tumour in the right breast, 4 suspicious axillary lymph nodes
  • Multiple suspicious lesions in bones and pleura
• Tumour biology: NST, ER 90%, PgR 70%, HER2 IHC 0, G2

Treatment with letrozole and CDK4/6i was started 1 month after diagnosis, which resulted in regression of bone and pleural metastases 3 months later and stable disease after 6 additional months.

Again 6 months later, i.e. 15 months after the start with letrozole and CDK4/6i:

• Imaging:
  • Pleura: stable disease, bones: progression, new liver metastasis
• Biopsy of liver metastasis: ER 70%, PgR 40%, HER2 IHC 0, G2
• Somatic PIK3CA mutation status: wild type
• Somatic ESR1 mutation status (on liquid biopsy): wild type
• Germline BRCA mutation status: wild type