Integrative clinico-genomic evaluation of the human epidermal growth factor receptor 2 (HER2) in urothelial cancer (UC).

4569 Background: HER2-directed therapy with trastuzumab deruxtecan is now FDA approved for UC with high HER2 expression. The interaction between HER2 expression, clinical phenotype and genomic tumor make-up is poorly understood in UC. Methods: We reviewed the records of 209 patients with UC and available HER2 expression status treated at MD Anderson Cancer Center between 2021 and 2024. Immunohistochemical (IHC) staining for HER2 and PD-L1 was conducted using 4B5 Ventana PATHWAY and 22C3 pharmDx antibodies, respectively. Formalin-fixed paraffin embedded metastatic or primary UC tumors were sequenced using the MD Anderson Mutation Analysis Precision Panel (MDA MAPP), a 610-gene high-throughput next generation sequencing (NGS) CLIA assay. Chi-square and wilcoxon tests were used to test correlations between HER2 expression and clinico-genomic features. P-values were adjusted for false-detection rate < 0.25. Results: We included 209 patients with available HER2 status (see Table). HER2 and PD-L1 had significant inverse correlation (p=0.0062). HER2 3+ status was significantly associated with bladder primary tumors compared to other sites (renal pelvis, ureter, and urethra) (p=0.0261). HER2 expression correlated with ERBB2 amplifications (0/1+: 0%, 2+: 2%, 3+: 26%, p<0.0001), but not with ERBB2 mutations. Of 13 patients with ERBB2 amplification, 12 were HER2 3+, and 1 was HER2 2+. HER2 also correlated with HELQ missense mutations (0/1+: 0%, 2+: 0%, 3+: 11%, p=0.0002), CDK12 alterations (0/1+: 0%, 2+: 0%, 3+: 20%, p=0.0003), and BCR missense mutations (0/1+: 0%, 2+: 0%, 3+: 11%, p=0.0002). Of 6 HER2 3+ patients with CDK12 amplification, all had ERBB2 amplification. Conclusions: Our study confirms prior observations of HER2 inverse correlation with PD-L1, but positive correlation with bladder origin. Beyond the known association with ERBB2 amplification, we identified molecular correlations between high HER2 expression, missense mutations of HELQ and BCR , and CDK12 alterations. The observed co-occurrence of CDK12 and ERBB2 amplifications may be related to their proximity (<267 kb apart) on chromosome 17q12. Only 26% of HER2 3+ patients had ERBB2 amplifications, highlighting the importance of IHC testing, not just NGS testing, to determine therapy candidacy for trastuzumab deruxtecan. HER2 Expression Status (n) 0/1+ (105) 2+ (58) 3+ (46) p value Primary tumor - Bladder, n (%) 74 (70) 43 (74) 41 (89) 0.0260 Primary tumor - Other, n (%) 31 (30) 15 (26) 5 (11) PD-L1 positive score, median % [IQR] 6 [1-30] 2 [1-10] 1.5 [0.75-5] 0.0062 ERBB2 amplifications, n (%) 0 (0) 1 (2) 12 (26) <0.0001 ERBB2 mutations, n (%) 10 (10) 8 (14) 9 (20) 0.2030 HELQ missense, n (%) 0 (0) 0 (0) 5 (11) 0.0002 CDK12 amplifications, n (%) 0 (0) 0 (0) 6 (13) <0.0001 CDK12 alterations, n (%) 0 (0) 0 (0) 9.2 (20) 0.0003 BCR missense, n (%) 0 (0) 0 (0) 5 (11) 0.0002