Some cancers start in one part of the body and spread to the skin. This is called skin (cutaneous) metastasis. In dogs and cats it is uncommon: a 2024 report of a dog whose lung cancer had spread to the skin was described by its authors as the first of its kind [1].
Have your vet check any new lump, sore or swollen toe on your pet. Other diseases can look the same, and only a vet can tell what it is.
Which cancers can spread to the skin
Published reports in dogs describe cancers of the bladder [2], the prostate [3] and the lung [1] reaching the skin. These are case reports and small case series, so they show that it can happen, not how often. In cats, lung tumors are the best known example and are covered below [4][5].
Signs on the skin
In a study of 12 dogs whose bladder cancer had spread to the skin, the skin changes were flat patches, small bumps or larger lumps, mostly on the belly, groin or the area around the genitals. In several of these dogs the surface over the lump had broken down into a sore [2]. In two dogs with prostate cancer, the spread showed up as several lumps on the skin of the belly or under the skin [3].
Other problems, such as infections and other lumps, can also cause bumps and sores on the skin. For lumps in general, see lumps and bumps on dogs and lumps and bumps on cats.
Cats: lung tumors that show up in the toes
Vets use the name “lung-digit syndrome” for a pattern seen in cats: a tumor that starts in the lung spreads through the blood and settles in the toes. The toes that carry weight are hit most often, and several toes or several feet can be involved at once. The lung tumor itself often causes no signs that owners notice, so the toe problem is what brings the cat to the vet [4]. Most affected cats are older [4]. The same kind of spread can also reach the skin and the muscles [4][5].
An affected toe tends to be swollen and red, with pus coming from around the nail and a nail that grows wrongly or sits pushed out. That looks a lot like a toe infection, so in a middle-aged or older cat a vet will also think about cancer that has spread [4]. Infections of the toes do happen and have a much better outlook, so they need to be ruled out too [5].
For other toe and claw problems, see nail and nail bed problems in dogs and cats.
How vets diagnose it
For cats with toe lesions like these, vets advise chest X-rays before any surgery on the toe, to look for a tumor in the lung [4]. Taking a sample with a fine needle, or a small biopsy, from the skin lump or the toe is usually much easier than sampling the lung, and together with X-rays it is often enough to reach a diagnosis [5]. In dogs, a sample of the skin lump looked at under the microscope helped point to where the cancer came from [3].
Treatment
Your vet will advise on care for your pet.
At home, as directed by a vet:
- do not pick at or squeeze any lump or sore;
- do not put human or leftover products on your pet’s skin or toes unless your vet says so;
- go back for every recheck your vet books.
Outlook
Cancer that has reached the skin has usually spread to other places as well. In the 12 dogs with bladder cancer, the cancer was also found in the lymph nodes of every dog and in other organs, mostly the lungs, in most of them, and survival after diagnosis was short [2]. For cats with lung-digit syndrome, the outlook is described as grave [4][5].
These are statements about groups of animals. They cannot predict how one pet will do. Your vet can explain what this means for your pet.
When to see your vet
See your vet if your dog or cat has:
- new lumps, bumps or patches on the skin, especially if they turn into sores [2][3];
- a swollen, red toe [4];
- pus from around a nail [4];
- a misshapen nail, or one that stays pushed out [4].
The bottom line
Cancer that spreads to the skin is uncommon in dogs and cats. In cats, lung tumors can show up in the toes. A new lump, sore or swollen toe can have other causes, and only a vet can find out what it is.
This article is for general information only and does not replace advice from your veterinarian. If your pet has a new lump, sore or swollen toe, see your vet.
Sources
- Greyling A, van der Weyden L, Lensink AV, O’Dell N. Pulmonary Adenocarcinoma with Cutaneous Metastasis in a Dog. Vet Sci. 2024;11(7):312. Open access, CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC11281710/
- Reed LT, Knapp DW, Miller MA. Cutaneous metastasis of transitional cell carcinoma in 12 dogs. Vet Pathol. 2013;50(4):676-81. PMID 23136183. https://pubmed.ncbi.nlm.nih.gov/23136183/
- Di Maria FM, Annoni M, Roccabianca P, Antoniazzi E, Bertazzolo W. Cutaneous metastases of prostatic adenocarcinoma in two dogs. Vet Clin Pathol. 2020;49(3):459-464. PMID 32865240. https://pubmed.ncbi.nlm.nih.gov/32865240/
- Goldfinch N, Argyle DJ. Feline lung-digit syndrome: unusual metastatic patterns of primary lung tumours in cats. J Feline Med Surg. 2012;14(3):202-8. PMID 22370862. https://pubmed.ncbi.nlm.nih.gov/22370862/
- Thrift E, Greenwell C, Turner AL, Harvey AM, Maher D, Malik R. Metastatic pulmonary carcinomas in cats (‘feline lung-digit syndrome’): further variations on a theme. JFMS Open Rep. 2017;3(1). Open access, CC BY-NC 3.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC5359792/