While all tumors need a blood supply to grow, some types of tumors have a propensity to create a very dense and active blood supply. Giant cell tumors, metastatic renal cell (kidney) and thyroid cancers, in particular, have abundant blood supply.
When these tumors are located in the spine or pelvis, the patient will often undergo "embolization" of the tumor before surgery. This significantly reduces the amount of blood loss at the time of surgery.
This procedure is performed by an interventional radiologist, i.e. a radiologist specially trained in performing invasive radiologic procedures. A small catheter is inserted into a large nearby artery, usually in the groin, and threaded carefully to the toward the tumor under x-ray guidance. Once there, the radiologist fills the vessel with tiny plastic beads which cut off the blood supply to the tumor.
The procedure can be done on an outpatient basis but, since it is typically done the day before surgery, the patient stays in the hospital overnight.

An example of preoperative embolization for a large, metastatic renal cell (kidney) tumor in the pelvis, note how effectively the ample blood supply to the tumor is reduced.