ERBB2 and breast cancer: With the new approval of trastuzumab deruxtecan for patients with HER2-low breast cancers (low expression defined as a score of 1+ or 2+ on IHC with negative FISH), there are a proportion of patients who may receive trastuzumab deruxtecan and sacituzumab govitecan sequentially in the triple negative or HR+ setting if their tumors carry low HER2 expression [54].