Final answer:
Cancer cells can proliferate without serum due to mutations that give them autonomy from growth signals normally supplied by serum. They overexpress receptors, produce growth factors, or have mutant signaling pathways, facilitating uncontrolled cell growth. This leads to their transformed state, characterized by a loss of contact inhibition, senescence evasion, and sustained angiogenesis.
Step-by-step explanation:
Cancer cells can proliferate in the absence of serum due to various mutations and alterations in normal cellular processes. Unlike normal cells that require serum as a source of growth factors, cancer cells often develop autonomy regarding these factors. A key feature of cancer cells is their ability to bypass the regulatory mechanisms that typically control cell division. Such transformations indicate that cancer cells have altered signaling pathways that no longer depend on the presence of growth factors found in the serum.
These alterations may include the overexpression of certain receptors, the production of their own growth factors, or mutations in the downstream signaling pathways that can trigger uncontrolled cell growth with much less external stimulus than is required for normal cells. This autonomy is a characteristic of their transformed state, which allows for continued division and growth, even when the conditions are not favorable, as would be the case in the absence of serum, which is usually essential for cell proliferation.
Furthermore, cancer cells are characterized by properties such as loss of contact inhibition, failure to undergo cellular senescence, and the acquisition of sustained angiogenesis. Loss of contact inhibition, for example, is facilitated by cancer cells' inability to form gap junctions and a reduction in adhesive proteins like integrins and cadherins, which normally enable cells to communicate their density and control growth accordingly. Coupled with their limitless replicative potential and ability to promote blood vessel growth (angiogenesis), cancer cells can grow and spread, or metastasize, more easily.