Molecular and immune landscape of FH-mutated cancers.

3125 Background: Fumarate Hydratase (FH) encodes an essential enzyme in the TCA cycle. Inactivating germline mutations in FH lead to hereditary leiomyomatosis and renal cell cancer syndrome with risk of development of certain cancers. Sporadic FH mutations have been described in different cancers but implications of somatic mutations on cancer outcomes and survival are not well described. Here, we characterize the molecular landscape of FH-mutant cancers. Methods: Tumors analyzed using NGS (NextSeq, 592 genes; NovaSeq, WES), IHC, and WTS (NovaSeq) (Caris Life Sciences, Phoenix, AZ). PD-L1 tested by 22c3, 28-8 (Agilent) and SP-142 (Spring Biosciences) IHC (>1%). MSI tested by FA, IHC, and NGS. TMB measured by totaling somatic mutations per tumor (TMB-h > 10 mutations/MB). Real-world overall survival was extracted from insurance claims data and calculated from first treatment to last contact using K-M survival curves for molecularly defined cohorts. Statistical significance was determined using chi-square and Wilcoxon rank-sum test, adjusted for multiple comparisons (q<0.05). Results: 3239 FH mutations were seen in 45 tumor types in 3149 FH-mutated tumors. NSCLC, colorectal and endometrial cancers harbored the most mutations. There were 839 pathogenic (P) or likely pathogenic (LP) and 2400 variants of unknown significance (VUS). Some tumors had multiple mutations. The most common mutations: R233H (P; 37), K477dup (LP; 555), and A41V (VUS; 70). VUS had increased TMB-H (40.4% vs 29.8%, q=0.004) and CREBBP mutations (5.1% vs 1.6%, q=0.012) compared to P+LP. A41V-mt tumors had significantly lower TMB-H than other VUS (8.8% vs 41.5%, q=0.002) and lower MSI-H (3.13% vs 3.69% vs 29.4%, q=0.003) and DICER1, PRKDC, FBXW7 mutations (q<0.05) compared to K477dup and R233. The A41V-mt patients had worse survival compared to patients with P+LP (HR: 1.4, 95% CI: 1.0-2.0, p = 0.049) and a trend toward worse survival compared to K477dup and R233H. In patients treated with chemotherapy, A41 was associated with worse survival compared to P+LP (HR: 4.6, 95% CI: 2.0-10.3, p<0.0001) and compared to K477dup and R233 (p<0.01). There was a trend towards worse survival after IO of A41-mt compared to P+LP (HR: 1.99, 95% CI: 0.88-4.5, p = 0.093). Conclusions: FH alterations are found in multiple cancers. A41V was the most common VUS mutation and is associated with a distinct molecular profile compared to K477dup-mt and R233-mt tumors; it was associated with worse survival in all-comers and after chemotherapy compared to P+LP mutations. This highlights the significance of this mutation and the need for further investigation into how this specific and other FH mutations contribute to cancer progression and treatment outcomes.