The veterinarians who claim that older animals are at an increased risk of anesthetic complications believe that as a pet ages it is more likely to accumulate problems such as heart valve insufficiencies, kidney damage or liver damage which make anesthesia a greater risk. I have repeatedly asked veterinarians which patients die most frequently from unexplained anesthetic crises and virtually all of them have lost a patient during a spay procedure, an ear crop or some other pediatric surgical procedure and very few can remember an incidence of anesthetic death in an older pet. Particularly if the better anesthetic agents are used. It is probably best to take lung X-rays and be sure the tumors haven't metastasized prior to surgery. Canine mammary tumors are benign most of the time but it is still a worthwhile precaution.
Mammary tumors grow unpredictably in size in dogs.
Some stay small for long periods of time and other grow so rapidly that it kills the tissue around the tumor and necrotic abscesses form. In most cases, your dog will enjoy a much higher quality of life without the tumors. Since mammary tumors seem to enlarge under the influence of the reproductive hormones it is best to spay a bitch at the time of mammary tumor removal. While there is no sure way of knowing it is very likely that tumor removal could extend her lifespan. Rises in alkaline phosphatase levels can occur for a number of reasons and Cushing's disease is only one of them.