2. This public good is assumed to be shared equally until "free-rider" clones (a concept derived from evolutionary game theory) arrive in the system and utilize the resources without contributing energy [in the form of ATP] to angiogenesis, and instead allocate resources towards proliferation.
3. This focus on proliferation allows the cheating clones a selection advantage, which out-competes the advantage of their angiogenic counterparts.
4. As cheater clones populate the tumor, cells grow further away from the oxygen source (as they are not secreting angiogenic factors) to which necrosis is inevitable.