HER2-Positive Gastrointestinal Cancers — Microlearning Activity 2: Proceedings from a Session Held Adjunct to the 2026 ASCO GI Cancers Symposium

For HER2+ gastric cancer patients with a single brain metastasis that is fully resected and radiated, experts may opt for close monitoring. This watch-and-wait approach is preferred over immediate systemic adjuvant therapy, even in this high-risk scenario.

Oncologists distinguish between HER2 amplification (the target for ADCs like TDXD) and activating mutations. A patient whose tumor loses amplification but retains a mutation is considered "HER2 mutated," not "HER2 positive," and is generally not a candidate for ADC therapy.

Patients with HER2-positive GI cancers can lose expression after treatment. While re-biopsy is ideal, it's often impractical or risky. In these cases, clinicians find ctDNA analysis of HER2 copy numbers to be a reliable alternative for guiding subsequent treatment decisions.

Interstitial Lung Disease (ILD) is a significant risk with TDXD. However, a history of a completely resolved grade 1 event does not automatically preclude a patient from receiving the drug again. Clinicians may consider a re-challenge, balancing the risk against the lack of other viable therapies.