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Why can a tumor not grow beyond a small size without angiogenesis?

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Precancerous growth in a human colon — cancer View through an endoscope of a polyp, a benign precancerous growth projecting from the inner lining of the colon.

A tumor is limited to a small size—typically 1 to 2 millimeters in diameter—because its cells become too distant from the essential nutrients and oxygen required for survival. Without the formation of new blood vessels, the tumor cannot receive the necessary supply to support further expansion.1

To overcome this limitation, tumors undergo angiogenesis, a process where they stimulate the growth of new capillaries by synthesizing specific growth factors, such as vascular endothelial growth factor (VEGF). This transition is a critical step in cancer progression, as it allows the tumor to move beyond a harmless cluster of cells and sustain its own growth in a semi-independent fashion. Once these vessels penetrate the tumor nodule, the endothelial cells and tumor cells begin to mutually stimulate each other, facilitating the tumor's transition to a life-threatening, malignant state.231