Cancer medicine is advancing at a breathtaking pace — but that speed is creating a new problem. As the FDA increasingly approves drugs for first-line use, oncologists are left with little to no evidence guiding what to prescribe when those therapies fail. The result, experts say, is a growing "evidence-free zone" where clinical decisions are made without guideline support or robust trial data.

The issue spans multiple cancer types and drug classes. In HER2-mutant non-small cell lung cancer, zongertinib moved from later-line to first-line approval in just 6 months, and sevabertinib followed a similar trajectory in 10 months — yet no data exists on optimal sequencing after either drug fails. In HER2-positive breast cancer, trastuzumab deruxtecan (T-DXd) has accumulated approvals across neoadjuvant, adjuvant, and metastatic settings so rapidly that standard second-line options were never tested in patients who received T-DXd first. Pembrolizumab's expansive approvals across colorectal, breast, and gastric cancers have created similar blind spots.

Key Takeaways:

• When first-line drugs fail, oncologists often must choose between options — another TKI, an ADC, or chemotherapy — with no head-to-head data to guide the decision
• Treatment inconsistency is expected to be significant, as clinicians acknowledge their approaches will vary considerably
• Insurance coverage for subsequent therapies is also uncertain when treatment sequences haven't been formally studied
• Individualized decision-making — weighing prior tolerability, toxicity profiles, and patient preferences — is currently the best available framework

Why it matters: As more drugs earn earlier-line approvals, the gap between what's available and what's evidence-supported will only widen. For patients and clinicians alike, navigating post-progression care is becoming one of oncology's most pressing — and underappreciated — challenges.