Skin signs can point to internal disease, and your vet looks for the cause. Nodular dermatofibrosis is a clear example. The firm skin nodules of this syndrome often come with cysts or tumors in the kidneys and, in female dogs, tumors of the uterus [1][4].
The skin nodules are often the reason a dog first sees a vet, while the kidney changes tend to show up later [1][4]. If your adult German Shepherd develops several firm lumps in the skin, have your vet check them and ask about the kidneys.
For other kinds of skin lumps, see our post on lumps and bumps on dogs.
What it is
Nodular dermatofibrosis is a rare inherited condition in which many firm nodules made mostly of dense collagen (the skin’s fibrous protein) form in and under the skin [1][2]. It was first described in German Shepherds, which remain the breed most often affected [1][5].
The kidney lesions range from cysts to cystadenomas and cystadenocarcinomas (tumors, benign or malignant, that form many fluid-filled cysts) [1][2]. Females can also have uterine leiomyomas (benign smooth-muscle tumors of the uterus) [1][5]. Researchers call the whole syndrome renal cystadenocarcinoma and nodular dermatofibrosis, or RCND [6][7].
How it is inherited
In a 1985 study of 43 German Shepherds, the authors traced the family trees and concluded that the syndrome is very likely inherited, most probably as an autosomal dominant trait, so one copy of the changed gene is enough [5]. A 2003 study linked the syndrome in German Shepherds to a change in the FLCN gene, which makes a protein called folliculin [6].
Not every case is the same
The syndrome has also been reported in other breeds, including Golden Retrievers, Boxers, Beagles, Australian Cattle Dogs and mixed-breed dogs [1][2]. Some of these dogs had a different gene change or none that could be found [2][3][8], and some had skin nodules without kidney or uterine changes [2][8]. A 2013 report described a Golden Retriever with the skin nodules, no kidney tumor on repeated ultrasound over 5 years of follow-up, and no change in the folliculin gene [8]. A 2019 report of a mixed-breed dog with the FLCN change suggested that the skin nodules may be a separate feature of the same genetic disease rather than a direct result of the kidney tumor [7].
What you may notice
- Many firm skin nodules: the nodules build up over time and can range from a few millimeters to several centimeters across [1][3]. They are mostly found on the legs and head [1].
- Leg problems: as the nodules progress they can lead to deformed limbs [1]. Sores on the feet or limping always need a vet check.
- Age: affected dogs are adults. In a 1997 study of 51 German Shepherds, the nodules were first noticed at 6.4 years of age on average [4].
- Kidney signs later: kidney lesions often become visible months to a couple of years after the skin nodules first bring the dog to the vet [1]. In the 1997 study, a vet could feel enlarged, misshapen kidneys in 60 per cent of the dogs [4].
In that 1997 study, skin lesions were the most common reason (37 per cent) owners brought their dog to a clinic [4]. This is why the skin nodules matter: they can be the first visible sign.
How it is diagnosed
- Examining the skin nodules: under the microscope the nodules consist mainly of dense collagen [1][5]. Like any lump, a nodule needs a vet check; your vet may take a needle sample or a biopsy [2].
- Checking the kidneys and uterus: case reports describe abdominal ultrasound to look at the kidneys and other organs, together with blood tests [1][2]. Your vet may also suggest urine tests.
- Genetic testing: the FLCN change can be tested for, but not every affected dog carries it [3][8]. Your vet can tell you whether testing is useful for your dog.
Treatment
There is no cure for this syndrome [1]. Authors of recent case reports suggest regular monitoring of the skin and kidneys over the long term [1][2]. Your vet will plan care for the skin nodules, any sores, and the kidneys and uterus, based on what the tests show.
Outlook
Outcomes vary between studies:
- A 2024 report notes that the outlook is generally poor, with many dogs dying or being put to sleep within about 2 years after the kidney tumors are found, and that dogs with kidney lesions on one side only, or none, tend to live longer [1].
- In the 1997 study of 51 German Shepherds, the average age at diagnosis was 8.2 years and the average age at death 9.3 years. The kidney lesions, including spread to other organs, were the main reason for death or euthanasia [4].
- In the 1985 study, the cancer had spread in 10 of the 23 dogs examined since 1979, and 10 of 11 females had several uterine leiomyomas [5].
- In the 2019 report, the dog was followed for 40 months after the kidney was removed, and the skin nodules grew in size and number over that time [7].
- In the 2024 report, a Beagle without the usual gene change was still alive 7 years after its first ultrasound [1].
These are figures and statements about groups of dogs or single dogs in particular studies. They do not prove that a treatment caused an outcome, and they cannot predict how one dog will do. Your vet can explain what the test results mean for your dog.
When to see your vet
See your vet if your dog has:
- several firm lumps in or under the skin [1][2]
- lumps on the legs or feet, sores on the feet, misshapen limbs or limping [1]
- any new lump on the skin
If your dog has been diagnosed with nodular dermatofibrosis, ask your vet how often the kidneys and, in females, the uterus should be checked [1][2].
FAQ
Are the skin nodules dangerous in themselves?
Biopsies of the nodules show dense collagen, not cancer [1][2]. The main concern is what they can point to: tumors of the kidneys and, in females, the uterus [4][5]. As they progress, nodules on the legs can lead to deformed limbs [1].
Is it only seen in German Shepherds?
No. German Shepherds are affected most often, but reports describe it in several other breeds and in mixed-breed dogs [1][2][3].
Is there a genetic test?
Yes, the FLCN change found in German Shepherds can be tested for [6], but some affected dogs of other breeds carry a different change or none that could be found [2][3][8]. Your vet can tell you whether testing is useful for your dog.
Can the kidney tumors be prevented?
No cure is known [1]. Regular checks of the kidneys are what case report authors suggest [1][2].
The bottom line
Skin signs can point to internal disease, and your vet looks for the cause. In nodular dermatofibrosis, multiple firm skin nodules in an adult dog, most often a German Shepherd, go together with kidney changes and, in females, uterine tumors [1][4][5]. The nodules often show up first [1][4], so have new skin lumps checked by your vet.
This article is for general information and does not replace a visit to your veterinarian. If you find lumps on your dog, contact your vet.
Sources
- Gómez-Barris BR, Balazs V, Villamar KC, Toro-Valdivieso C. First case of nodular dermatofibrosis with cystic renal disease in a beagle: An atypical case without FLCN gene mutation. Vet Med Sci. 2024;10(2):e1401. Open access, CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC10918974/
- Lee K, Nam C, Dan T, Lee K, Park H. Case Report: Atypical Nodular Dermatofibrosis and Renal Cysts in a Bichon Frise with a BRCA2 Mutation and No FLCN Mutation. Animals (Basel). 2025;15(14):2070. Open access, CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC12291678/
- Schneiter M, Selz J, Jonker J, et al. FLCN Multi-Exon Deletion in a Chihuahua With Renal Cysts and Nodular Dermatofibrosis. Anim Genet. 2026;57(5):e70215. Open access, CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC13621923/
- Moe L, Lium B. Hereditary multifocal renal cystadenocarcinomas and nodular dermatofibrosis in 51 German shepherd dogs. J Small Anim Pract. 1997;38(11):498-505. https://pubmed.ncbi.nlm.nih.gov/9403809/
- Lium B, Moe L. Hereditary multifocal renal cystadenocarcinomas and nodular dermatofibrosis in the German shepherd dog: macroscopic and histopathologic changes. Vet Pathol. 1985;22(5):447-455. https://pubmed.ncbi.nlm.nih.gov/4049673/
- Lingaas F, Comstock KE, Kirkness EF, et al. A mutation in the canine BHD gene is associated with hereditary multifocal renal cystadenocarcinoma and nodular dermatofibrosis in the German Shepherd dog. Hum Mol Genet. 2003;12(23):3043-3053. https://pubmed.ncbi.nlm.nih.gov/14532326/
- Ciccarelli S, Di Bello A, Valastro C, et al. Unilateral renal cystadenocarcinoma and nodular dermatofibrosis in a mixed-breed dog carrying a FLCN gene mutation. Vet Dermatol. 2019. https://pubmed.ncbi.nlm.nih.gov/30672048/
- Zanatta M, Bettini G, Scarpa F, et al. Nodular dermatofibrosis in a dog without a renal tumour or a mutation in the folliculin gene. J Comp Pathol. 2013;148(2-3):248-251. https://pubmed.ncbi.nlm.nih.gov/22871425/