Integrated morphological, immunohistochemical, and genomic profiling identifies uterine leiomyoma patients with hereditary leiomyomatosis and renal cell cancer syndrome: a comprehensive analysis of 252 cases.

Fumarate hydratase-deficient uterine leiomyomas (FHd-ULMs) represent a molecularly distinct subgroup of smooth muscle tumours associated with hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome. This study determined the detection rate of germline pathogenic FH variants in FHd-ULMs using paired tumour-normal sequencing and assessed the utility of integrated morphological, immunohistochemical (FH/2SC), genomic, and clinical features for selecting cases suspected of HLRCC. Histopathological assessment of the 252 FHd-ULMs revealed consistent morphological features, whereas molecular profiling identified three biologically distinct categories. Germline FH-mutated (hereditary) cases constituted 35.7% (74/207) of this FHd-ULM cohort, four of which showed concomitant somatic copy-number alterations. This contrasted with the somatic-mutated subgroup, which comprised 50.7% (105/207), including 18.4% (38/207) with isolated somatic copy-number losses. The remaining 13.6% (28/207), though lacking detectable FH mutations, were classified with somatic-mutated cases as sporadic FHd-ULMs based on shared clinicopathological features. Molecular analysis identified shared variant distributions across exons 2-10, with exons 5 and 7 in the fumarate lyase domain emerging as the predominant mutational hotspots. Notably, truncating mutations showed significantly higher prevalence in hereditary cases versus somatic variants (p < 0.01). Clinically, hereditary FHd-ULMs presented at younger ages (< 45 years) and manifested more aggressive phenotypes, including elevated rates of infertility (54.1% versus 26.4%), multifocal tumour development (86.5% versus 53.4%), increased surgical interventions (44.6% versus 11.5%), and familial leiomyoma clustering (51.4% versus 24.2%). Our results identify germline FH mutations, which confer significant HLRCC risk, in 35.7% of FHd-ULMs, while somatic alterations account for the majority of cases. To ensure efficient resource allocation, we propose a stratified diagnostic approach: initial universal FH/2SC immunohistochemical screening for ULMs displaying ≥ 3 FH-deficient morphological features, followed by confirmatory genetic testing in high-risk individuals, defined by either aberrant FH/2SC immunoreactivity or, in immunohistochemically normal cases, age < 45 years together with a personal/family history of multiple symptomatic leiomyomas or HLRCC-associated neoplasms. © 2026 The Pathological Society of Great Britain and Ireland.