In patients with liver metastases, a low tumor fraction can cause false-negative liquid biopsy (ctDNA) results. Clinicians recommend obtaining a tissue biopsy to confirm the absence of targetable mutations and ensure concordance, preventing misinformed treatment decisions based on potentially inaccurate ctDNA.
Experts theorize that because resistance to PI3K inhibitors often involves downstream AKT activation, subsequent use of an AKT inhibitor is logical. However, re-challenging the pathway with a PI3K/mTOR agent like getatolisib after an AKT inhibitor has already failed is seen as less rational based on pathway biology.
Preclinical data suggests tumors with PTEN loss develop a heightened dependence on the mTOR pathway. This provides a strong biological rationale for selecting an mTOR inhibitor, like getatolisib, over an AKT or PI3K inhibitor in this specific patient subpopulation for potentially better efficacy.
Experts question the biological validity of the one-year cutoff for recurrence after adjuvant Aromatase Inhibitor (AI) therapy, a common clinical trial inclusion criterion. They suggest that clinical judgment should be applied, as the biological reality of resistance is not a binary switch at 12 months.
Beyond specific pathway alterations like ESR1 or PIK3CA, clinicians view a concurrent TP53 mutation as a robust marker of aggressive disease biology. This common finding is used to justify choosing more aggressive combination therapies over potentially less effective single-agent approaches.
For patients with aggressive, rapidly progressing disease, clinicians use serial ctDNA monitoring between scheduled imaging scans. A rising ctDNA tumor fraction can serve as an early warning sign of treatment failure, allowing for quicker therapeutic pivots before the cancer grows significantly.
When a patient exhibits slow, indolent ('grumbling') progression on a first-line CDK4/6 inhibitor, clinicians may opt to continue with a different CDK4/6 inhibitor combined with fulvestrant. This strategy prioritizes quality of life and defers more toxic or novel therapies for later lines.
Experts are enthusiastic about a future paradigm where treatment is adjusted based on detecting emerging resistance mutations (like ESR1) via liquid biopsy before clinical progression occurs. This proactive approach aims to target small resistance clones early, potentially improving long-term outcomes.