**12. Conclusion**

We summarized our research regarding a familial thyroid follicular cell carcinoma in Dutch German longhaired pointer dogs. We identified two deleterious mutations

in the *TPO* gene that confer great relative risk in homozygous status. A genetic test was developed and made commercially available for breeders and owners of GLPs. We expect to greatly diminish the incidence of the familial FCC in GLPs by using this genetic test and will help to eradicate the familial FCC from the GLP population. Furthermore, we identified a recurrent somatic mutation, the *GNAS* p.A204D, in the familial FCCs with a prevalence of 62.5%. Identification of this somatic mutation implicates the role of GPCR-mediated molecular signaling pathways in the FCC initiation and development. With a high prevalence of the *GNAS* p.A204D somatic mutation, those affected dogs might serve as a good disease model to understand the pathogenesis of tumors associated with *GNAS* somatic mutations and to test novel treatments that targets on tumors with *GNAS* somatic mutations.
