Clinicopathological and molecular characteristics of fumarate hydratase–deficient uterine smooth muscle tumors: a single-center study of 52 cases

The fumarate hydratase (FH) gene germline mutations cause hereditary leiomyomatosis and renal cell carcinoma syndrome (HLRCC), predisposing carriers to uterine and cutaneous leiomyomas and renal cell carcinoma. In this study, we aim to investigate morphology and the correlation between FH mutation in FH-deficient (FH-d) uterine smooth muscle tumors (uSMTs). We conducted immunohistochemical staining in 161 cases of uSMTs to detect FH deficiency. We identified 52 cases (52/161, 32%) of FH-d, including 34 leiomyomas with bizarre nuclei, 10 uSMTs of uncertain malignant potential (STUMPs), 4 cellular leiomyomas, 3 usual type leiomyomas, and 1 leiomyosarcoma. Patients with FH-d were aged 24–67 years (median, 40 years). The most common FH-d morphological features included staghorn-shaped blood vessels (87%), bizarre nuclei (81%), alveolar pattern edema (65%), macronucleoli surrounded by a halo (65%), cytoplasmic eosinophilic globules (56%), and chain-like distribution of smooth muscle cells (52%). A targeted next-generation sequence was performed in 11 of 52 FH-d tumors. Five cases (5/11, 45%) were found with FH germline mutations, including 4 leiomyomas with bizarre nuclei and 1 STUMP. The median age of patients with germline FH mutation was 30 years. The germline mutations included 3 pathogenic, 1 likely pathogenic, and 1 rare uncertain clinical significance variants. Our results revealed that FH-d uSMTs usually exhibit the distinct morphology features and high frequency of FH germline mutations. The combination of predictive morphology evaluation, FH immunotype, and molecular testing is helpful for the screening of HLRCC in uSMTs.