Tumors of the spleen are common for older large breeds and we see this often at the shelter. If your dog is in good health as determined by lab work and X-rays I see no reason to not do the surgery. Generally the entire spleen is removed. We usually biopsy the organ and it is determined if the tumor is benign or malignant. If benign no follow up chemotherapy is usually done. If malignant chemotherapy is recommended. You may actually extend your dogs quality lifespan.

Remember if your dog has a bad reaction to chemotherapy you do not have to continue treatment. The surgery alone will extend quality life. Unfortunately, we do not usually extend life of those with malignancy for more than a year at best, some for as little as 2 months.