Breast Cancer

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A breast cancer is a malignant collection of cells that form a tumour, originating from one of the cells in the breast. ‘Breast cancer’ refers to several types of cancer of the breast, with ductal carcinoma[1] being the most common.

There are two main types of breast cancer which are due to a single gene mutation in genes which code for DNA repair proteins BRCA-1 and BRCA-2. These are both tumour-suppressor genes and are key parts of the DNA-break repair systems, therefore they are unable to repair DNA where the homologous chromosome is providing template repair. These 2 proteins are accessory proteins - they are non-essential for homologous recombination (if they were essential the cell would undergo apoptosis). Instead, there is a gradual build-up of damage to the DNA due to these mutated proteins not properly repairing the DNA. If a women inherits one mutated allele of BRCA-1, they have a 60% probability of developing breast cancer by the age of 50, compared with a 2% probability if a women has two normal alleles. These statistics lend themselves to the genetic influence on cancer. However most types of breast cancer are due to a several low penetrance genes instead as cancer is an example of a polygenic disease, therefore it is a disease where many genes are involved.

The genetic prediction of breast cancer susceptibility is varied depending on which type of breast cancer we are talking about, advice can be given to those with a family history due to BRCA-1 or BRCA-2. But for other types of breast cancer it is hard to advise women on their risk due to so many factors and the effects of individual’s polymorphisms[2][3][4].


  1. National Cancer Institute. (2017). Breast Cancer. [online] Available at: [Accessed 6 Dec. 2017].
  2. Alberts et al (2008) Molecular Biology of the Cell, 5th Edition, New York: Garland Science. Chapter 5, page 310
  3. Alberts, Johnson, Lewis, Raff, Roberts and Walter (2008) Molecular Biology of The Cell, fifth edition, New York: Garland Science.
  4. Lodish, Berk, Kaiser, Krieger, Scott and Bretscher (2008) Molecular Cell Biology, sixth edition, New York: W. H. Freeman and Company.

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