I am so sorry to hear about your boy. I lost my beloved Daisy to hemangiosarcoma (HSA) in 2005. She had an undetected tumor that ruptured and was removed and biopsied. The results of the tests were negative for HSA; she died less than a month later when she started bleeding again and they found that the cancer had covered her insides. I learned that there are a significant number of false negatives.
HSAs grow quickly but as I understand typically don't metastasize until they rupture. Then the cancer cells are seeded in all the internal organs and take off like wildfire.
My best advice is to brace yourself. Please forgive me for being direct, but I was led to have hope where little existed, and I was not prepared when I lost my girl. HSA is wicked, wildly aggressive, and unless things have changed in the last 3 years, current chemo treatments only add days, not years.
THAT IS NOT TO SAY THAT THERE IS NO HOPE BUT YOU MUST ACT QUICKLY! I DO suggest that you look into the Navy protocol - see link:
You are fortunate to live in a state with some mighty fine vet schools. Or perhaps you could take him to Tufts in Boston. But if you intend to take action, DO NOT DELAY. DON'T WAIT FOR THE TEST RESULTS. CALL THEM TODAY!
Here is a link to a website that discusses alternative therapies and any and every piece of advice about HSA, and the thread I participated in (sorry, this is the link I have bookmarked, but you can get to other threads from there. It will be painful to read.) http://theherbs.info/Pets/jennifer.html
One favor...PLEASE, PLEASE see links below about sharing some of your dog's blood with researchers studying HSA. We lose dogs so quickly to this wretched disease, and researchers need samples from dogs with the disease to be able to create diagnostics and cures.
These are 2 I could locate quickly. Perhaps your vet or oncologist will know how best you can help. I wish I would've known about these before Daisy died. It pained me that I missed that opportunity to give her heartbreaking loss some meaning.
You are on top of this from the get-go, and that may make ALL the difference for your dog, and hopefully many others. I hope you will be fortunate to change the future for all of us.
My heart goes out to you.