Prospective Fumarate Hydratase Tumor Predisposition Syndrome Screening in Patients With Uterine Smooth Muscle Tumors: Age, Morphology, Fumarate Hydratase/S-(2-succino) Cysteine Immunohistochemistry, and Germline Testing.

Fumarate hydratase tumor predisposition syndrome (FHTPS) is caused by germline fumarate hydratase (FH) pathogenic variants (PVs). Most women with FHTPS develop FH-deficient (FHD) uterine leiomyomas (ULs), which arise 10 to 15 years earlier than aggressive FHD-renal cell carcinoma. We evaluate a previously proposed FHTPS screening strategy for women with ULs. This 5-year, prospective and retrospective study performed FH and later S-(2-succino) cysteine immunohistochemistry (IHC) on all uterine smooth muscle (USM) tumors in patients 40 (later ≤30) years or younger and on all USM tumors with suggestive FHD morphology regardless of age. Patients with FHD tumors by IHC were referred to genetic counseling. Of 840 USM tumors, 112 FHD-tumors by IHC (13%) were identified, all with suggestive FHD-morphology; 44 patients (39%) underwent germline testing, and 15 harbored germline FH PVs (34.1% of germline tested, 13.4% of all FHD-tumors). While FHD tumors were seen across a wide age range (24 to 73 y), those with germline FH PVs were significantly younger (median 33 vs 44 years wild-type, P = 0.0032). Few (12.5%) patients ≥40 and no patients ≥50 had a germline FH PV, whereas a majority (60%) of patients <40 (86% of those <30) had a germline FH PV. We demonstrate that previously proposed resource-conscious screening involving morphology and IHC is effective for identifying women with FHTPS. We provide prospective data confirming patients presenting with FHD-ULs over age 50 are unlikely to harbor germline FH PVs and argue that for germline testing without consideration of other factors, a threshold of younger than 50 years may be appropriate.