β-Catenin Mutation Status and Outcomes in Sporadic Desmoid Tumors

Background. Mutations in the gene-encoding beta-catenin, CTNNB1, are highly prevalent in sporadic desmoid tumors and may predict the risk for recurrence. We sought to determine the prevalence of CTNNB1 mutations in a large cohort of sporadic desmoid tumors and to determine whether CTNNB1 mutation status correlates with disease outcome. Methods. Single-base extension genotyping of the CTNNB1 gene was performed on 145 sporadic, paraffin-embedded desmoid tumor specimens. Correlation of mutation status with outcome was performed on a subset of 115 patients who underwent macroscopically complete surgical resection. Results. CTNNB1mutationsweredetected in 106 of 145(73%) tumor specimens and in 86 of 115 (75%) specimens from patients who underwent curative-intent surgical resection, including discrete mutations in the following codons of CTNNB1 exon 3: T41A (46%), S45F (25%), S45P (1.7%), and S45C (0.9%). Desmoid tumors of the superficial trunk were significantly less likely to harbor CTNNB1 mutations than tumors located elsewhere, but none of the other examined clinicopathologic factors were found to be associated with CTNNB1 mutation status. At a median follow-up of 31 months, 5-year recurrence-free survival was slightly, although not statistically significantly, worse for patients with beta-catenin-mutated tumors than for those with wild-type tumors (58% vs. 74%, respectively). The specific CTNNB1 codon mutation did not correlate with the risk for recurrence. Conclusion. CTNNB1 mutations are indeed common in sporadic desmoid tumors. However, our study did not detect a statistically significant difference in recurrence risk according to either the CTNNB1 mutation status or the specific CTNNB1 mutation.