Is cancer an evolutionary system? | Sean B. Carroll

Key Concepts

• Evolutionary Disease: Cancer as a process driven by natural selection at the cellular level.
• Mutations: Changes in DNA that can confer a growth advantage to cells.
• Tumor: A population of unregulated growing cells.
• Genetic Diversity: The increasing variation in mutations within a tumor over time.
• Oncogenes/Tumor Suppressor Genes: Genes involved in controlling cell growth.

Cancer as an Evolutionary Process

Cancer is fundamentally an evolutionary disease, mirroring the principles of natural selection. This process begins with mutations occurring in individual cells. If these mutations provide a growth advantage to the affected cells, they will outcompete their neighboring cells. This competitive advantage can lead to further mutations, amplifying the growth advantage and resulting in the formation of a tumor. A tumor is defined as a population of cells that grows in an unregulated manner compared to its normal counterparts.

The Threat of Unregulated Growth and Tumor Progression

The unregulated growth characteristic of tumors poses a significant threat. This uncontrolled proliferation can lead to the cancer spreading throughout the body, affecting various organs, and ultimately causing death. Furthermore, as a tumor grows larger, individual cells within it accumulate additional mutations. This ongoing accumulation of mutations means that over time, the tumor becomes increasingly dissimilar to the cell from which it originated. Crucially, this process leads to greater genetic diversity within the tumor itself.

Age and Cancer Risk: The Role of Cell Division and Mutation Accumulation

The risk of developing cancer increases significantly with age, particularly in individuals in their 40s, 50s, 60s, and 70s. This correlation is directly linked to the evolutionary nature of cancer. As individuals age, their cells undergo more divisions. Each cell division presents an opportunity for mutations to occur. Over a lifetime, cells have had more chances to accumulate mutations that grant them a growth advantage over other cells. This accumulation of advantageous mutations is a primary driver of increased cancer risk in older age groups.

Cancer as a Genetic Disease: Disrupting Cell Growth Control

The observation that cancer risk increases with age and is driven by mutations underscores its nature as a genetic disease. Cancer arises from mutations occurring in specific genes that are responsible for regulating normal cell growth. When these genes are disrupted by mutations, the intricate mechanisms that control cell division and proliferation are compromised, leading to the uncontrolled growth characteristic of cancer.

The Search for Cancer-Causing Genes

A major area of scientific interest and research is the identification of these critical genes involved in cancer development. Understanding "what are those genes?" and "how do we find them?" is central to developing effective diagnostic and therapeutic strategies. The goal is to unravel the complex genetic pathways that, when mutated, lead to the initiation and progression of cancer.

Conclusion

In essence, cancer is a disease driven by evolutionary principles operating at the cellular level. Mutations conferring growth advantages lead to unregulated cell proliferation, forming tumors. The genetic diversity within tumors increases over time, and the cumulative effect of mutations from repeated cell divisions throughout an individual's life significantly elevates cancer risk with age. The focus of cancer research is to identify the specific genes involved in these processes to better understand and combat the disease.