Are you planning to start running IHC HER2 testing on all tumor types, even those where HER2 overexpression is less typical, in light of tumor agnostic approval of trastuzumab deruxtecan?

In my practice, I recommend HER2 IHC testing for all patients with advanced cancers, especially for those with epithelial cancers. For patients in whom HER2 positivity is rare, I also take into account any concerns about tissue availability as well as clinical eligibility for HER2-targeted therapy.

The recent tumor-agnostic approval of trastuzumab deruxtecan (T-DXd) has shifted the landscape of HER2 testing strategy. Historically, HER2 evaluation was confined to tumor types with precedent—breast, gastric, and later lung and colorectal cancers.

The question now is how to incorporate HER2 testing...

Testing for HER2 status has become essential beyond breast, colon, and gastric cancers. HER2 amplification or overexpression can occur in other solid tumors such as lung, colorectal, bladder, biliary cancers, etc. I am personally testing for HER2 overexpression/amplification for almost everything no...

Standard testing per IHC was required for entry onto the clinical trial that led to trastuzumab deruxtecan approval across cancer types.

Meric-Bernstam et al., PMID 37870536

Please note HER2 'grading' was per upper GI cancer criteria.
NGS can identify HER2 amplification by both DNA and RNA profiling. ...