Unilateral renal cystadenocarcinoma and nodular dermatofibrosis in a mixed-breed dog carrying a FLCN gene mutation

Background Renal cystadenocarcinoma and nodular dermatofibrosis (RCND) is a rare inherited cancer syndrome observed predominantly in the German shepherd dog breed, known to be associated with dominant autosomal transmission of mutation H255R of the encoding folliculin gene (FLCN). The syndrome usually features bilateral, multifocal kidney tumours and skin nodules, consisting of dense collagen fibres, with previous reports showing a poor prognosis. Although historically nodular dermatofibrosis (ND) has been considered a paraneoplastic syndrome associated with renal cystadenocarcinoma; this hypothesis has been questioned. Objectives To report a case of unilateral renal adenocarcinoma in a dog with RCND syndrome, with 40-month follow-up. Animal A neutered 5-year-old female, mixed-breed dog. Methods and materials Nodular dermatofibrosis was confirmed with histopathological evaluation. Contrast-enhanced ultrasound (CEUS) supported a presumptive diagnosis of unilateral renal neoplasia and the kidney was removed. Results Nodular dermatofibrosis with unilateral RC was confirmed by histopathological evaluation and DNA sequencing; this was positive for the heterozygous form for the H255R mutation in the FLCN gene. Follow-up at 40 months after nephrectomy showed progressive increase in the size and number of nodular lesions. Conclusion and clinical importance This case supports the hypothesis that nodular dermatofibrosis is not a paraneoplastic syndrome associated with cystadenocarcinoma. It may be instead an independent dermatological feature of the same genetic disease, linked to the mutation of FLCN given that the cutaneous nodules in this dog increased in size and number after removal of the adenocarcinoma.