Hello, my name isXXXXX and I have over 20 years of experience as a veterinarian.
I'm sorry to hear that your pup has a mass on her spleen.
Is this mass palpable on abdominal palpation?
Was it seen on radiographs or an abdominal ultrasound?
Are there any metastases seen on radiographs of her chest and abdomen?
The most common tumor we see on the spleen, especially in German Shepherds, and Golden Retrievers is a hemangiosarcoma. These tumors are very, very aggressive and usually have metastasized by the time we find the primary tumor, even if we cannot see the metastases on radiographs or ultrasound. But if we see metastases then the prognosis is even more guarded.
Usual treatment is surgical removal of the spleen to remove the primary tumor and then chemotherapy. But honestly even with that sort of aggressive treatment these pups rarely have a good quality of life for any length of time or a lifespan longer then 6 months.
With no treatment they usually have weeks to months.
These tumors usually rupture at some point as they tend to grow quickly and outgrow their blood supply, which leads to an abrupt drop in blood pressure and sudden death.
Another option is a homeopathic treatment with a product called I'm-Yunity which is derived from a particular mushroom that has had some very promising results.
Here are some links to read about a study done at Penn as well as the company's website to buy the product.
Best of luck with your pup, please let me know if you have any further questions.