Answer:
Angiogenesis.
Step-by-step explanation:
Angiogenesis can be defined as biological process, which involves formation of new blood vessels.
Angiogenesis helps tumors by forming new blood vessels that feed the developing tumors by providing them nutrients and oxygen. It allows the tumor to enlarge and cancerous cells to metastases (invading nearby tissues and cells).
Thus, the correct answer is 'Angiogenesis.'