Dogs develop many types of skin lumps, most of which aren't cause for concern, but a few are cancer lumps and should be immediately evaluated by a veterinarian.
Lymphoma
Lymphoma is a common dog cancer that can occur in the liver, spleen, lymph nodes and other organs. Those that occur in the lymph nodes are often seen on the skin. However, you may be able to feel other internal lumps with regular inspections. Tumors may develop in the lymph nodes and swell, but cause no other symptoms. Additional symptoms include itching, redness and ulcers around the tumor. Treatment usually involves removal of the tumor, radiation treatment and/or chemotherapy, which can have varying degrees of success. Treatment is usually less effective on lymphoma of the skin.
Sarcoma Tumors
Two common types are fibrosarcoma and hemangiosarcoma. Both are associated with the skin and are very aggressive. Since they may spread quickly, immediate action is required. Most veterinarians recommend removal, even if that means large chunks of muscle and bone. Amputations may also be required.
Fibrosarcoma is usually associated with vaccinations or injections and forms at that site, most commonly in between the dog's shoulder bones, where they receive most injections. These tumors form strange shapes and are very firm.
Hemangiosarcoma are usually caused by sun damage and may appear on the chest or abdomen. They often ulcerate and are usually dark in color.
Mast Cell Tumors
This is another common cancer that exhibits itself in the form of tumors. In this case, one or more tumors may be present, varying in size and location. Some mast cell tumors are very small and easily overlooked. They may appear smooth, bumpy or ulcerated and may be dark or discolored.
Mast cell tumors are usually grouped into grades, which vary from level 1 to 4. Level 1 are the most slow-growing while level 4 are fast-growing and likely to metastasize. Treatment and prognosis vary largely on the grade of cancer and the advancement of the tumor.
Cell Carcinoma
Another common type of tumor is squamous cell carcinoma, which is commonly associated with sun damage or chronic skin problems. These tumors may appear one of two ways: cauliflower-shaped lesions that are commonly ulcerated and appear most commonly on the lips and nose or larger, crusty ulcers that appear on the legs or other parts of the body where skin irritation may occur. Treatment of these tumors may involve surgical removal or radiation, depending on the location.
Basal Cell Tumors
Many types of tumors that appear on your dog's body can be cancerous or benign. Basal cell tumors are an example of this. Though this type of tumors is a cause for concern, it may also be benign. Basal cell tumors form into lumps, often around your dog's head, neck or chest. They may be fluid-filled, causing them to feel squishy, or dark in color, but this is not always the case. Because these tumors don't often metastasize, they can usually be removed, if cancerous, without requiring chemotherapy.
Histiocytosis
There are three forms of histiocytosis, and only one of them is malignant. However, all three look similar, forming large, hairless nodules, which usually have ulcers. The malignant form affects both the skin and internal organs and has no known effective treatment.