Roundtable Roundup: Biomarker-Guided Therapy for HR+ Breast Cancer

CASE SUMMARY

• A 52-year-old postmenopausal woman had a history of grade 2, node-negative invasive ductal carcinoma (IDC).
• Estrogen receptor positive (ER+) and progesterone receptor positive (PR+); HER2 immunohistochemistry (IHC) 0; Ki-67 20% of the right breast; 21-gene recurrence score, 27
• Initial therapy included chemotherapy, radiation therapy, and 5 years of adjuvant anastrozole.
• Three years after completing anastrozole, metastatic progression was discovered, including symptomatic bone involvement (multiple vertebrae and bilateral iliac crests).
  • Bone marrow aspiration confirmed ER+/PR+, HER2 IHC 0, stage IV IDC.

• ECOG performance status: 1
• Mild anemia

• The patient started letrozole and ribociclib (Kisqali) with denosumab (Xgeva), with good clinical response and marked improvement in her pain.
• She required 1 dose reduction to 400 mg of ribociclib due to neutropenia.
• Twenty months after starting therapy, routine staging scans showed new fluorodeoxyglucose-avid sclerotic and lytic bone lesions.
  • She noted mild increase in lower back pain.
  • Laboratory studies were normal.
• Circulating tumor DNA (ctDNA) analysis confirmed an ESR1 mutation.
• No evidence of PIK3CA/AKT1/PTEN mutations