Angiogenesis and Cancer
Blood vessels "feed" cancer cells by supplying oxygen and nutrients. Without this supply, the tumor would starve and eventually 'die'. Tumors were found to release growth hormones to promote angiogenesis and attract blood vessels. The need for blood vessel supply is a hallmark of every type of cancer and likely plays a role in the progression of most solid tumors.
In support of this finding, in immunohistochemistry sections one can often see a denser network of blood vessels around the tumor compared to healthy tissue.