Digital tumors (tumors of the toe or canine digit) tend to be diagnosed only after months of mistreatment with antibiotics when an infection is wrongly suspected.
My hope is that after learning the most common signs of digital tumors it will allow you to receive a more timely diagnosis (and better prognosis) if your dog (or a friend's dog) is ever to experience a digital tumor.
The most common signs of digital (toe) tumors
The most common signs in dogs with digital tumors are the presence of a wound, mass +/- lameness (limping/favoring the affected limb). Affected dogs are typically older, with a median (half older and half younger) age of 10 years.
If your dog has a digital mass or an ulcerated toe or nail bed wound that isn't healing, get a biopsy. Many cases of digital cancer go undiagnosed for months while round after round of antibiotics are tried to no avail. Seventy-three percent of digital tumors are malignant; we want to get an accurate diagnosis as soon as possible.
Most common types of digital (toe) tumors & affected breeds
Squamous cell carcinoma (SCC) is the most common digital tumor in dogs followed by malignant melanoma.
Other digital tumors include: soft tissue sarcoma, mast cell tumor, osteosarcoma, adenocarcinoma, plasma cell tumors, lymphoma, chondrosarcoma, synovial cell sarcoma. *Basically any type of cancer can affect the digit; benign tumors are also possible. Remember that 73% of digital tumors are malignant (only 27% are benign).
A small number of dogs with squamous cell carcinoma (3%) will experience multiple digits affected at the same time. Patients are typically large breed dogs with black skin and haircoat such as standard poodles, black Labradors, giant schnauzers, Gordon setters, and Rottweilers. Dachshunds and flat coat retrievers may also be predisposed to digital SCC.
Scottish terriers appear more likely to develop malignant melanoma of the digit than other breeds.
Digital tumors can metastasize, so appropriate work-up (staging) is important at the time of diagnosis (before surgery or other treatment).
Staging should include: 3-view thoracic radiographs read by a board certified radiologist (chest x-rays), full blood work (CBC, chemistry), urinalysis, aspiration and cytology of the draining lymph node, +/- abdominal ultrasound.
In dogs with digital SCC, 8.8% had evidence of metastasis (spread to other organs) at the time of diagnosis and an additional 23.2% developed metastasis at a later time.
In dogs with digital malignant melanoma, 28% had metastasis at the time of diagnosis with an additional 38.5% developing metastasis at a later time.
If cancer is confined to the toe, surgery is recommended. Surgery typically consists of removing the affected digit ("digit amputation"); sometimes it consists of removing more than one digit in order to remove all cancer cells. And of course, sometimes it's a bit more complicated than this, so it's always a good idea to have an oncologist weigh in on the best treatment for your dog's tumor.
Digit amputation (versus just removing skin) is required for malignant digital tumors because in the vast majority of cases of SCC and melanoma, the tumor has invaded the bone of the digit. X-rays (radiographs) are not a sensitive method of ruling out bone involvement; if x-rays don't show bone destruction it doesn't meant that there aren't tumor cells invading bone.
Dogs do fine with removal of a digit. In many cases two digits can be removed, and in many cases, this is needed to remove all cancer cells. This is a good scenario to have a board certified oncologist +/- surgeon to weigh in on the best treatment strategy.
If cancer is confined to the toe and a neighboring lymph node, surgery to remove the affected digit and affected lymph node is recommended. In these cases, since cancer has metastasized (spread), systemic treatment is needed after surgery to help slow the spread of cancer (to other lymph nodes and organs). In the case of SCC systemic treatment consists of chemotherapy (ex. carboplatin). In the case of melanoma systemic treatment normally consists of the melanoma vaccine, but some oncologists prefer chemotherapy.
Prognosis (how long a dog will live) depends on the (1) type of tumor (2) treatment pursued (3) success of treatment pursued (4) characteristics of the specific type of tumor (when the pathologist evaluates the tumor, do they see evidence of tumor cells in blood vessels or lymphatics, do they see many "mitotic figures", etc., (5) if metastasis occurred.
It seems that dogs with SCC arising from the nail bed (this is called "subungual") will live significantly longer than SCC arising from other parts of the digit. Studies have shown that 95% of dogs with subungual SCC will be alive 1-year after diagnosis and 74% will be alive 2-years after diagnosis (if treated with surgery, provided no metastasis at diagnosis).
If the SCC arises from a different part of the digit, 60% will be alive 1-year after diagnosis and 40% will be alive 2 years after diagnosis (if treated with surgery, provided no metastasis at diagnosis).
One-year survival rates for dogs with malignant melanoma range from 42-57%, and 2-year survival rates range from 13-36%. Again, these are for patients that are treated with surgery that do not have any evidence of metastasis at diagnosis.
In my experience, dogs with malignant melanoma of the digit that have lymph node metastasis will only live a few months, even if treated with surgery and the melanoma vaccine.
A study showed that dogs with malignant melanoma treated with the melanoma vaccine and surgery did have a longer survival than dogs without the vaccine.
The melanoma vaccine can be a good option for dogs with digital melanoma (and melanoma in other locations). It is given only by oncologists. One vaccine is given every other week for four treatments, then every six months thereafter. We typically administer the vaccine in the inner thigh. The vaccine is very well tolerated. We typically have clients monitor the injection site for redness for the first few days after injection. I've never had a patient feel "unwell" after the vaccine, as is typical for traditional vaccines.
**It's important to know that the vaccine is only meant to work in a "microscopic disease" setting. This means that the vaccine is meant to be used after surgery to help kill microscopic cancer cells that are expected to exist in blood vessels and lymphatics. The vaccine should not be used in place of surgery.
If your dog develops lameness, check his feet and toenails for abnormalities. If he develops a wound on any of his digits, you can try a short course of antibiotics, but if there isn't improvement after 7 days of antibiotics (plus and e-collar to prevent licking), get a biopsy. There are always more treatment options and a better prognosis if a tumor is detected early.
Dr. Lori Cesario
Board Certified Veterinary Oncologist
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