Abstract 1457: Somatic biallelic inactivation of fumarate hydratase (FH) in uterine leiomyomas
Authors: Tolvanen Jaana , Mäkinen Netta , Heinonen Hanna-Riikka , Bramante Simona , Mehine Miika , Sarvilinna Nanna , Sjöberg Jari , Heikinheimo Oskari , Pasanen Annukka , Bützow Ralf , Aaltonen Lauri A. 
Published: July 2017

Uterine leiomyomas (ULMs) are highly common benign tumors that affect the health of millions of women by causing a variety of symptoms. Furthermore, ULMs are the most common indication for hysterectomy, generating considerable economic costs for the health care system. Recurrent and mutually exclusive genetic aberrations leading to unique gene expression profiles have been identified in ULMs. Thus these tumors can be divided into distinct subclasses according to their molecular genetic background.

The majority of ULMs (80-90%) have specific mutations in MED12 or aberrations in HMGA2. Somatic biallelic inactivation of FH can also, albeit rarely, drive ULM tumorigenesis and has previously been detected in 1.3% of sporadic ULM samples (2/153; Lehtonen et al, 2004).

FH encodes the fumarase enzyme that catalyzes the hydration of fumarate to L-malate in the tricarboxylic acid cycle. Biallelic inactivation of FH leads to accumulation of fumarate and aberrant succination of proteins. Heterozygous germline FH mutations predispose to a rare autosomal dominant tumor predisposition syndrome, hereditary leiomyomatosis and renal cell cancer (HLRCC). This highly penetrant syndrome is characterized by uterine and cutaneous leiomyomas and in some cases renal cell cancer.

In this study, we re-evaluated the frequency of somatic biallelic inactivation of FH in ULMs in the largest sample set thus far. The study material consisted of 1167 fresh frozen ULM and their respective normal myometrium tissue samples from 375 hysterectomy patients. All samples were analyzed with high-throughput SNP array (Infinium Human Core-24+ Kit, Illumina Inc., San Diego, CA). All tumors detected with somatic deletions or loss of heterozygosity (LOH) in the FH locus were included in S-(2-succinyl) cysteine (2SC) immunohistochemistry (IHC) to indirectly detect biallelic FH inactivation. Also samples without FH double deletions were selected for Sanger sequencing of FH coding regions to detect inactivating mutations.

Somatic FH deletions or LOH were detected in 30 tumors, of which 10 were identified FH deficient by 2SC IHC. In these samples, another deletion (a double deletion) in three ULMs and a somatic nucleotide change in six ULMs was found to be the second hit causing biallelic inactivation of FH. In one sample no second hit was detected with these methods. From the six somatic nucleotide changes, four were different FH missense mutations predicted to be damaging (SIFT, PolyPhen-2, Provean) and two were synonymous substitutions in the last nucleotide of different exons. Studies to determine the impact of these synonymous changes on splicing are underway.

To conclude, in our sample set we detected 0.9% (10/1167) of the ULMs to harbour somatic biallelic inactivation of FH. MED12 exon 1 or 2 mutations and HMGA2 rearrangements were not detected in these tumors. Thus the previously published results were validated in this study with the largest sample set so far.

Citation Format: Jaana Tolvanen, Netta Mäkinen, Hanna-Riikka Heinonen, Simona Bramante, Miika Mehine, Nanna Sarvilinna, Jari Sjöberg, Oskari Heikinheimo, Annukka Pasanen, Ralf Bützow, Lauri A. Aaltonen. Somatic biallelic inactivation of fumarate hydratase (FH) in uterine leiomyomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1457. doi:10.1158/1538-7445.AM2017-1457