Hemangiosarcoma is a nasty cancer which often remains undetected until it's a dire emergency when the tumor bursts causing severe internal bleeding. My brother-in-law's dog died from it.
By the time symptoms show up, the tumor is usually very large and has metastasized.
So far there is no way to screen for this. Tufts University is running a trial to determine whether certain isoenzymes, found to significantly increase in dogs with some types of cancer, particularly hemangiosarcoma, could serve as good biomarkers for early detection.
Having a good way to screen for it before it blows up on you would certainly be great.
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