Genetic Testing – Larry Seymour, MD

genetic testingA few days ago I was sitting in my favorite hospital coffee shop breaking my morning fast (after a test) and heard two people walking by say: “Genes are everything”. Yes, they are, particularly in cancer.

We are all born with about 20,000 genes, and this is our “germ line”. Each gene has its location on the strand of DNA. Genetic testing is used to check this DNA strand for variants which might predispose to cancer as in some kinds of breast cancer. This testing is done with saliva, or a cheek swab or a blood sample. No doubt you’ve seen testing like that on TV.

Genomic testing is done to find the gene changes that have occurred during life due to sun exposure, or tobacco smoke among many factors, some unknown. Most of these changes don’t cause problems, but certainly the two mentioned do. Testing is done the same way.

Genomic profiling tests cancer cells for the DNA changes that have occurred just in the cancer itself. Testing reveals gene abnormalities that cause cancer growth, but it turns out there are many abnormalities in some cancers. This testing is not routinely done for three reasons: 1) It frequently doesn’t give information anyone can act on at this time; 2) It is very expensive (sticker shock is the word); 3) The routine process of testing the cancer in the lab after surgery destroys the DNA in the cancer so this tissue is now not usable for this specialized testing.

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