Whole Genome and Transcriptome Tumor Sequencing to Identify Predictors of Sensitivity to Sequential Sacituzumab Govitecan (SG) Following Trastuzumab Deruxtecan (T-DXd) Treatment in ER+/HER-2 Low Metastatic Breast Cancer
Advanced hormone positive (HR+), HER2 negative breast cancer continues to pose a challenge when patients have progressed on CDK4/6 inhibitor and endocrine therapy leaving limited treatment options. Antibody-drug conjugates (ADCs) such as sacituzumab govitecan (SG) and trastuzumab deruxtecan (T-DXd) have changed practice due to significant improvement in progression free survival (PFS) and overall survival (OS) seen in this disease setting. There is a genuine interest to use SG sequentially after T-DXd, however there is no current prospectively curated evidence to support this strategy. Though the epitope is different, the payload are both topoisomerase I inhibitors. Thus, evidence is needed of both clinical efficacy and identification of mechanisms of sensitivity and resistance to sequential ADCs in HER-2 low MBC. It is hypothesized that performing whole genome and whole transcriptome sequencing in fresh tumour biopsies post progression of T-DXd and prior to SG in ER+/HER2 low metastatic breast cancer (MBC) will provide mechanistic insights into identifying biomarkers, and thus patients, sensitive to sequential SG.
• Patients must meet all of the following inclusion criteria to be eligible for participation in this study:
• Willing and able to provide signed informed consent approved by UBC/BC Cancer REB
• Female or male patients, regardless of race and ethnic group, who are ≥18 years old at the time of informed consent
• Patients with locally advanced or metastatic ER+/HER2 low (defined as IHC 1+ or 2+ but FISH or CISH negative by ratio as per ASCO/CAP guidelines) breast cancer. Patients with imaging confirmed inoperable locally advanced breast cancer for which treatment is palliative in intent are also permitted.
• Prior treatment must have included prior endocrine based treatment in the metastatic setting in conjunction with a CDK4/6 inhibitor.
• Prior treatment must include at least 1 line of chemotherapy which must include trastuzumab deruxtecan (T-DXd) as the immediate prior line of therapy prior to study enrollment
• The tumour must be accessible to be able to safely perform image guided biopsies for WGS and WTS.
• Negative serum pregnancy test at baseline for pre-menopausal patients (within 14 days prior to randomization) and agreement to use medically approved precautions to prevent pregnancy during the study and for 12 weeks following the last dose of SG
• Patients can have measurable or non measurable (but assessable) disease by CT or MRI as per RECIST Version 1.1 criteria as evaluated locally. Tumor lesions situated in a previously irradiated area are considered measurable if unequivocal progression has been documented in such lesions since radiation.
• ECOG PS 0-2
⁃ Life expectancy ≥ 3 months
⁃ Acceptable bone marrow and organ function defined by the following laboratory values:
∙ Absolute neutrophil count ≥1.0 x 109/L
‣ Platelets ≥100 x 109/L
‣ Hemoglobin ≥9.0 g/dL
‣ INR ≤1.5
‣ Serum creatinine clearance \>50 mL/min
‣ In absence of liver metastases, direct bilirubin ≤1.5 x ULN, ALT and AST should be below ≤2.5 x ULN. If the patient has liver metastases, ALT and AST should be \< 5.0 x ULN.
⁃ Controlled brain metastasis (as per clinical determination) is allowed in the study at least 4 weeks before treatment. (Controlled brain metastasis is defined as no longer symptomatic from brain metastasis or no longer requiring higher doses of corticosteroids (\> 10 mg Dexamethasone per day) for CNS management. Anticonvulsants and stable corticosteroids dose can be included in the study).