Genetic testing

As a result of the identification of a number of mutated genes in hereditary non-polyposis colon cancer - MSH2, MSH1,

PMS1 and PMS2, and in breast and ovarian cancer - BRCA1 and 2, the genetic testing of individuals for common cancers has become a reality. As over 20% of all cases of breast cancer have a family history (usually only a mother or aunt with the disease), breast cancer has become the spearhead for genetic testing. In the study of a family with a suspected inherited genetic disorder, it is best to define the mutation of the disease gene which, as it may only affect one base-pair, requires sequencing of the whole gene from an index case. For a large gene such as BRCA1 this is impracticable, but likely sites of mutation have been identified on which limited sequencing can be performed. Having identified the specific mutation, it can be sought in other members of the family. For the genetic testing of 'familial' rather than dominantly inherited cancer: for example those with one or two first-degree relatives affected, a less specific test seeking alterations in the expressed product (e.g. a 'protein trunction test') can be used.

The indiscriminate use of genetic testing is to be avoided. Young women, knowing that they have a family history of breast cancer, must be made aware of the benefits and risks before having a test and care should be taken to minimize psychological distress, stigmatization and discrimination. This has led to the development of the genetic clinic where a geneticist with the support of a nurse counsellor will compile a detailed family pedigree, recognizing that most people have knowledge of at most two generations. At this clinic the woman should be fully informed about the concept of inheritance, the extent to which this contributes to general population risk and the benefits and risks of genetic testing. This should include the nature of the gene to be tested, its mode of inheritance and associated cancer risk, and the advantages and limitations of the test to be used. The implications of a positive test must be fully described, in particular the effect it might have on employment and insurance. Potential monitoring or preventative measures should be explained.

Emotional and psychological support may be necessary at this first session. Should serious anxiety be identified, a psychiatric assessment may be advised. Blood may be collected at this first attendance, recognizing that if the patient is uncertain and wishes further counselling before agreeing to have the test, the specimen can be stored.

In some clinics this initial attendance is followed up by a letter which reviews the information which has been given, reinforces the concept of inheritance, the benefits and risks of genetic testing and likely recommendations should the test prove positive. If blood has been collected at the first visit, consent for the test to proceed may be given at this stage.

Once the result of the test is known, further counselling is necessary. The risks to the woman and her female offspring and other close relatives is reviewed. Should the test prove positive, alternative measures to monitor the breasts and the possibility of prophylactic surgery are explained. Consultation with a surgeon can be arranged so that the pros and cons of prophylactic mastectomy can be assessed, recognizing that even this cannot completely remove all risk.

Figure 9.12. The metastatic cascade.
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