PRACTICAL GENETICS
ROLE OF GENETICS IN CANCER DIAGNOSIS AND MANAGEMENT
AUTHORS Jasdeep Singh Sidhu , MD , MBBS & Vikas K . Singh , MD
Cancer develops when cells divide uncontrollably as a result of alterations in genes that regulate their growth . Therefore , all cancers can be called “ genetic ” because they involve changes in the genetic material . These genetic changes ( aka mutations ) arise due to various factors . Most cancers are sporadic ( 75-80 %), as when these mutations are acquired during someone ’ s lifetime . The risk of developing cancer in these individuals is usually influenced by their medical and lifestyle factors ( i . e ., smoking , sun / radiation exposure , chemicals , some bacteria / viruses , etc .).
Other common causes are familial factors , which account for 15-20 % of all cancers . In this group , the cancer does not seem to be caused by a change in one gene , rather a result of multiple influences . A combination of several genes and other factors such as diet and exercise , all contribute a small amount to an inherited increase in the family ’ s risk of developing cancers . Researchers do not yet have the capability to test these genes or pinpoint the cause ( s ) of their mutation ( s ). Therefore , testing is not possible in the majority of cases with a familial factor as part of overall risk .
Only a small percentage of cancers , 5-10 %, are truly inherited . Inherited cancers are caused when the cancer-causing gene mutations are passed from one generation to another . This gene mutation , also called germline mutation , could be either in the egg or sperm from which the person was conceived and is present in all cells of the body . Individuals with these inherited mutations have a higher risk of developing cancers at a young age . Each of their children has a 50 % chance of inheriting the gene mutation .
The most well-known association between cancers and genetic abnormalities is in the case of Chronic Myeloid Leukemia ( CML ). Chromosomal Translocation between long arms of chromosome 9 and chromosome 22 , aka “ the Philadelphia chromosome ,” was the first chromosomal abnormality known to be associated with a malignancy ( it is present in over 96 % cases of CML ). The known association between certain hereditary cancer syndromes and genetic mutations can be helpful to assess the risk of a particular cancer in family members of a patient . Genetic testing is now available for a number of rare hereditary cancers especially those associated with single gene disorders such as APC gene mutation associated with Familial Adenomatous Polyposis , MLH1 and MSH2 with Lynch Syndrome and BRCA1 and 2 with familial breast cancer , ovarian
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