Fig. 2: Association between time to next treatment (TTNT) for patients treated with trastuzumab deruxtecan (T-DXd) and tissue-based HER2 quantification using HS-HER2, HER2DX ERBB2, and RPPA HER2.

Samples are ordered by HER2 IHC subtype and TTNT from the start of T-DXd treatment. Clinical parameters displayed include HER2 IHC subtype (HER2-zero, HER2-low, HER2-positive), latest HER2 IHC prior to T-DXd, number of prior lines of chemotherapy, and receipt of sacituzumab govitecan before T-DXd. An asterisk on the TTNT bar indicates treatment is still ongoing. Bar plots show scores for each assay, and these values are also represented with color-coded squares, along with their corresponding quartiles for the HS-HER2 and RPPA HER2 assays. For HER2DX ERBB2, score groups are displayed based on the recommended cutoffs: Low (1–32), Med (33–50), and High (51–99)²¹. Some cases are depicted as HER2-positive given prior HER2-positivity, despite the closest biopsy to T-DXd administration being formally HER2-negative (as suggested by the IHC score). HS-HER2, High Sensitivity-human epidermal growth factor receptor 2; RPPA, Reverse Phase Protein Array; T-DXd, trastuzumab deruxtecan; TTNT, time to next treatment. *did not experience TTNT event.