| Location: | Toes/sole of the foot |
| Behaviour: | Between oral melanomas and skin melanomas, frequent metastases (> 50%) |
| Diagnostics: | Needle aspirate/lymph node removal, radiography (bone and chest cavity) |
| Treatment: | Primary tumor: surgery and additional radiotherapy |
| Prognosis: | Strongly depending on the stage and treatment method used |
In terms of malignant behavior, this tumor type is in between oral melanomas and skin melanomas. Metastases to local lymph nodes and lungs occur in 58-71% of cases, 5% of the melanomas on the toes lead to bone damage to the underlying bone.
These melanomas can grow in the nail bed or on the sole of the foot. It can take different forms: a small growth, a poorly demarcated swelling of the involved toe, an ulcerated growth.
Swelling of the toes is often one of the first symptoms to notice. Some dogs will lose a nail or limp on that paw. In general, these tumors are black.
A fine needle aspirate from the mass as well as from the local lymph nodes should be performed.
X-rays of the affected toe should be taken to estimate whether the melanoma has affected the bone. X-rays of the lungs are also important to estimate the presence of metastases.
Surgery is the most appropriate treatment for local melanomas. If the melanoma is on the nail bed, it may be necessary to amputate the entire toe due to bone damage. Footpad melanoma can lead to full limb amputation, as full weight may be resting on the affected footpad and removal of the footpad will result in a loss of use of that leg.
Radiotherapy is an efficient alternative for tumors that cannot be (completely) surgically removed. Melanomas generally respond well to radiotherapy administered in high doses (1x / week, four times). A possible side effect of this treatment is loss of nails or sloughing of the sole of the foot. The nails and soles of the feet will regrow and will not cause long-term problems.
Carboplatin chemotherapy may be useful to delay or prevent the spread of metastases. However, there are no published studies yet that show that chemotherapy leads to an extended survival time. The standard chemotherapy protocol is a combination of carboplatin with surgery and / or radiotherapy. Carboplatin is administered intravenously every 3 weeks for a total of 4 treatments. The side effects are minimal.
About 50% of the melanomas of the nail bed and the soles of the feet spread to the other parts of the body. If the mitotic index is <3, the tumor is more likely to behave benignly and there is a lower risk of metastasis. The treatment of a local relapse has a less good prognosis than the treatment of the original tumor. The chance of local relapse is 14-30%. The mean survival time is 12 months, 1 year after diagnosis an average of 42-66% of the dogs are alive, 2 years after diagnosis an average of 12-22%.
