When patients present with both ESR1 and PI3K mutations, treatment selection isn't based on a definitive molecular test. Instead, oncologists make a clinical judgment, inferring the dominant resistance pathway from factors like the duration of prior therapy to guide their choice of targeted agent.

The four TCGA molecular profiles (e.g., POLE-mutated, p53-abnormal) have evolved beyond predicting outcomes to actively guiding treatment, such as de-escalating therapy for low-risk groups and escalating for high-risk ones.

A key distinction for oncologists is that PIK3CA mutations are typically "truncal" (present from baseline), whereas ESR1 mutations are "acquired" after exposure to aromatase inhibitors. This biological difference dictates when and how to test for each biomarker throughout a patient's treatment journey.

Because POLE testing often requires a send-out NGS test, the turnaround time is slow. Clinicians report they cannot wait for these results and must make treatment decisions, such as starting chemotherapy for a p53-mutant tumor, before the full molecular profile, including the crucial POLE status, is known.

Oncologists are more comfortable using a positive ctDNA test to escalate care (e.g., recommend chemo for a low-risk Stage II patient). However, they are more hesitant to use a negative test to de-escalate or withhold standard chemo for higher-risk patients, pending more definitive trial data.

While clinicians often ponder how to prioritize treatments for patients with multiple actionable biomarkers, this scenario is exceedingly rare in practice. The guiding principle, if it does occur, is to choose the therapy with the strongest supporting clinical trial data, though this remains an infrequent dilemma.

Experts advise against using gene expression profiling to escalate care for CSCC (e.g., deciding to add systemic therapy). Its primary utility is in de-escalation: a low-risk profile can provide an additional data point to support a decision for observation in a borderline high-risk case, helping to avoid overtreatment.

A nuanced approach to PARP inhibitors involves reserving combinations for BRCA2 patients with clear, aggressive clinical features like high-volume disease or liver metastases. This strategy balances potent efficacy against toxicity for a molecularly defined but clinically heterogeneous group, avoiding overtreatment of those with more indolent disease.

TP53-mutated AML carries an extremely poor prognosis, significantly worse than other adverse-risk subtypes. When TP53 patients are excluded from analyses, the survival gap between the remaining adverse-risk and intermediate-risk patients narrows considerably, clarifying risk stratification.