To complicate matters, it is clear that the changes needed to create a cancer cell can be accomplished in many different ways. Although all cancers have to overcome the same spectrum of regulatory functions in order to grow and progress, the genes involved may differ. In addition, the order in which the genes become de-regulated or lost may also vary. As an example, colon cancer tumors from two different individuals may involve very different sets of tumor suppressors and oncogenes, even though the outcome (cancer) is the same.
The great heterogeneity seen in cancer, even those of the same organ, means that diagnosis and treatment are complicated. Current advances in the molecular classification of tumors should allow the rational design of treatment protocols based on the actual genes involved in any given case. New diagnostic tests may involve the screening of hundreds or thousands of genes to create a personalized profile of the tumor in an individual. This information should allow for the tailoring of cancer treatments geared to the individual. For more information on this see the Genomics/Proteomics section.
The genetic changes that lead to unregulated cell growth may be acquired in two different ways. It is possible that the mutation can occur gradually over a number of years, leading to the development of a 'sporadic' case of cancer. Alternatively, it is possible to inherit dysfunctional genes leading to the development of a familial form of a particular cancer type. Some examples of cancers with known hereditary components include:
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Breast cancer- Inheritance of mutant versions of the BRCA1 and BRCA2 genes are known risk factors. Although many, if not most, individuals with breast cancer do not have detectable alterations in these genes, having a mutant form increases the likelihood of developing breast cancer.
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Colon cancer- Defects in DNA repair genes such as MSH2 are known to predispose individuals to hereditary non-polyposis colorectal cancer (HNPCC).
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Retinoblastoma- Defects in the Rb tumor suppressor gene are known to cause this eye cancer and several other types of cancers. More on this particular disease can be found in the chapter on Rb
This is an incomplete list of the known inherited cancer types, and it is certain that more inherited forms of cancer will identified as the genetics of various types of cancer are clarified.
More information on this topic may be found in Chapters 2 and 4 of The Biology of Cancer by Robert A. Weinberg.
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