Cancer is heterogeneous diseases and it has extraordinary potential to survive even in adverse conditions (for e.g. hypoxia in the cancer cell). So its survival after these hurdles raises the question whether the transformation of a normal cell into cancer cell is evolutionary process or not?
I would say that cancer is most certainly an evolutionary process. It fits all the criteria such as competing for space and resources even cooperating to ensure survival and is based on mutation and selection. Heterogeneity is a reflection of all these processes acting on individual cancer cells at any one time.
Some scholarship argues that Carcinogenesis should be viewed as speciation due to the autonomous and genomic changes that occur in cancers. (article attached)
S. Huxley, famous evolutioanry biologist once wrote, "once the neoplastic process has crossed the threshold of autonomy, the resultant tumor can logically be regarded as a new biological species."
So tumors autonomous battle with our immune system may be viewed as an argument for speciation.
http://www.ncbi.nlm.nih.gov/pubmed/1383781
Cancer most certainly represents an evolutionary process. Your own definitions agree with this...1) acquired mutations....giving a selective advantage over neighbours, these are inherited by daughter cells which themselves mutate and the process is repeated. 2) Environment pressuring populations of cells to adapt or favouring some over others. These are all definitions of evolution.
I think you are misunderstanding the context of evolution in the question....it wasnt does cancer provide a selective advantage for the host in the human population but of cells against their neighbours within tissues.
I think the difference in opinions here can be accounted for based on the angle you take (evolutionary process for an entire population vs. an evolutionary process on the cellular level within an individual).
Indeed, this is also what I think. Oncogenesis is genetic and epigenetic adaptation of "selfish" cells to an adverse environment. The question that drives me is, what made the environment adverse so that the solution to the "organism" cancer cell was to revert its differentiation. Is hypoxia the reason or are their other players such as the immune system or apoptosis?
This is definately an important aspect of change , which..when gives you a better result is evolution but when it is a cause of compromise to the normal function is a disease. Somatic cell mutation dont effect the next generation,,,,,cancers are the result of mutations which are random and continous. this is an effect of change but dont lead to evolution
Answer may depend on what we define as a subject of evolution. if it is a establishment of a new specie, then cancer cells are not new species which may exist on its own, as they would need a scientist to keep them alive. From that prospective, malignant cells are results of probabalistic behaviour of cells in a human body. Therefore, the malignant cells may be on the way to evolve, but I have not heard about a new specie "Homo.cancer"....
However, if the subject of evolution is a cell, then cancer cells are evolution...
What do you think?
@Serhiy, that is a very good point, depending on how we define the "population" we could say that cancerous cells are an evolutionary extent of the precursor somatic cells. However, from a different angle, one would not be able to make those assertions.
@Abdalla,
Defining mutated cells is not necessary for determining whether or not cancer represents an evolutionary process.
Simply, the marked changes in the genome may be seen as evidence for potential speciation associated with carcinogenesis.
Additionally, from a scientific angle, it is easily defined.
mutation as a change in nucleotide sequence of the genome.
However, I think you are trying to ask a metaphysical question.
The comparison to evolution does provide some insights into cancer etiology. In my view, cancer develops from mutation (inherited or somatic) followed by selection that drives a mutator phenotype to escape normal regulation by senescence or apoptosis. However evolution acts at the level of the organism and cancer selection acts at the cell level and this is an important distinction.
Our group has been working on the cancer evolution for many years now.
The key to study cancer evolution is to understand the two phases of somatic cell evolution. Stepwise slow evolution (where gene mutation and epigenetic change dominate), and punctuated macroevolution (or revolution, if you will) (where the genome re-organization is the driving force).
In addition, evolution can be observed from multiple levels.
For more info about somatic cell evolution and cancer, please see our reviews:
Chromosomal instability (CIN): what it is and why it is crucial to cancer evolution.
http://www.ncbi.nlm.nih.gov/pubmed/23605440
Evolutionary mechanisms and diversity in cancer.
http://www.ncbi.nlm.nih.gov/pubmed/21925306
For the organismal evolution, please see:
Sex reduces genetic variation: a multidisciplinary review.
http://www.ncbi.nlm.nih.gov/pubmed/21091466
Evolution takes several years to proceed but cancer cell can form within hours to months, which is most devastating example to distinguish the cancer in the context of evolution.
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