Has anyone had a dog that was diagnosed with a hemangiosarcoma in the thigh muscle only and if so what was the outcome?

This would be a fairly rare presentation of a hemangiOSarcome, so there may not be anyone else who can tell you how their dog's case turned out.

HemangiOSarcoma is an invasive tumor that arises from the cells lining blood vessels. The most common sites are in the spleen and around the base of the heart. Treatment generally consists of attempting to remove as much of the tumor as possible, which is great if the tumor is localized to just the thigh. Dogs tend to do pretty well with only three legs - you can ask anyone who has worked with rescued racing greyhounds about this.

The bad part about hemangiOSarcomas is that they try to make new blood vessels branching off of the existing cardiovascular system. The new blood vessels are very weak, and can rupture at any time. If the tumor is not removed, your dog may live anywhere between another few minutes and another few years - but every time you leave the house you risk coming back and seeing that your dog has died from the weak tumor blood vessels rupturing. Running, jumping and playing would increase this risk, as blood pressure would increase and you would have increased mechanical stress on the vessels as well.

German Shepherds and Gold Retrievers appear to have a higher risk of developing hemangiOSarcomas. The tragic part about this type of cancer is the first symptom is generally "I left for work and he was fine, I came back home and he was dead". The death is very rapid due to bleeding out internally.