I have an 11 year old bassett that has cancer. A few years ago he had a small cancerous tumor on his belly that was removed and healed well. Recently he developed a tumor on the roof of his mouth. It is a very rapid progressing type of cancer. He has had laser surgery once. The cancer has spread to his entire mouth within less than 6 weeks. He does not act as if he is in pain and continues to be active; however his mouth bleed often and sometimes excessively. The vet also noticed a lump around his shoulder and informed us that more than likely he has cancer in his lungs. Bassett's are prone to cancer, especially if they are in the sun a lot or have a lot of white color on them. We will soon have to put ours to rest. I hope yours lives along healthy life. Take yours to the vet ASAP.
Your dog is suffering from "sarcoma tumor". Proper medication can cure it. In extreme case you will have to go for surgery. Anti-viral medicines can help your dog to get rid of this lump. Take your dog to vet will suggest some medicine.