Unlike tamoxifen, oral SERDs likely cannot be used as a monotherapy in premenopausal women. The pre-CoAbera trial failed to show gerodestrant alone was sufficient and was associated with ovarian cysts and higher estradiol. This suggests ovarian function suppression (OFS) is a necessary partner for oral SERDs to be effective in this younger patient population.
Despite emerging trial data, clinicians are not yet ready to change therapy based on ctDNA positivity alone. Key concerns cited include the absence of a proven survival benefit from early intervention, the potential to use future treatment lines prematurely, and overall feasibility. The consensus is that while promising, the technology is not yet ready for routine clinical decision-making.
The TRACK-ER study reveals a critical weakness of tumor-informed ctDNA monitoring: a 16% failure rate. This occurs when there's insufficient tumor tissue or too few personalized variants to track. This technical barrier poses a significant obstacle to widespread clinical implementation, highlighting the need for more robust or alternative assay technologies for all patients to benefit.
The SERENA-6 study reveals that ESR1 mutations, a key resistance mechanism, emerge steadily throughout first-line aromatase inhibitor and CDK4/6 inhibitor therapy. This finding indicates that a single ctDNA test is inadequate. Instead, a strategy of continuous, serial monitoring is necessary to detect molecular relapse in real-time, posing a new paradigm for patient management.
The debate over the SERENA-6 trial centers not on drug efficacy, but on its unique design. Intervening at molecular relapse (ESR1 mutation) instead of clinical progression creates a new patient population that doesn't fit neatly into first-line maintenance or second-line treatment categories. This ambiguity complicates regulatory interpretation and defining the appropriate control arm.
The TRACK-ER study shows ctDNA positivity isn't just a future risk predictor. Nearly half (44%) of patients with a newly positive ctDNA test were found to have metastatic disease on imaging. This suggests ctDNA often detects existing, micrometastatic disease that standard scans miss, challenging the distinction between early-stage surveillance and managing overt metastatic cancer.