The genetics of cancer

“Is cancer passed down through our genes?

If a relative has cancer, is my risk of getting cancer any higher?

If it is genetic, and I get cancer, what are the chances that I will pass it on?

Are there any tests out there for these things?”

These are all questions I found myself wondering last weekend as I worked on capsule slides in the Microbiology lab, while all the cool kids were out getting wasted.

That was when I realized I had found the topic of my second blog post for Senior Seminar.
I also realized I could really use a liquid cocaine shot.

So I started searching for answers as the snow began to pour down outside.

According to this informative website by the National Cancer Institute, “all cancer is genetic”.
What they mean by that is that all cancer arises from mutations in DNA, or altered genes. When the genes that regulate and control a cell are messed up, the cell is unable to stop replicating. It takes many steps, but if subsequent mutations occur and certain conditions are met, the cancerous cell will progress from normal, to malignant (dangerous), to metastatic (spreading).

“Cancer usually arises in a single cell. The cell's progress from normal to malignant to metastatic appears to involve a series of distinct changes in the tumor and its immediate environment, and each is influenced by different sets of genes.”[1]

But disease inheritance is very complex. Altered or damaged genes do not always get expressed in harmful ways. Different mutations, or the same mutation at different locations, will have different effects. Some will be expressed by severe symptoms, some as mild symptoms, and others will not be expressed at all.

As it turns out, cancer can be passed down if that specific damaged or mutated gene (disease-linked gene) gets passed on. If careful records are kept, a family tree mapping the expression of the disease-linked gene can be constructed. This is helpful in determining your chances of inheriting a disease-linked gene.

[http://www.cancer.gov/cancertopics/understandingcancer/genetesting/Slide24]

The good news is, most cancer is NOT inherited.
“Even though all cancer is genetic, just a small portion--perhaps 5 or 10 percent--is inherited.” [1]

This means that out of ten breast cancer patients, only one of them may have a known inherited factor. The other nine also have cancer, but due to unknown factors that are not inherited.

The Human Genome Project has successfully mapped the chemical bases of all 25,000 genes, as well as the spaces between them.
“This information can be used to determine where gene mutations occur in specific diseases.”[1]
For example, here is a chart of disease-linked genes located along the X chromosome.

With Microarray analysis, complete patterns of gene activity can be captured.
“A DNA microarray is a thin-sized chip that has been spotted at fixed locations with thousands of single-stranded DNA fragments corresponding to various genes of interest. A single microarray may contain 10,000 or more spots, each containing pieces of DNA from a different gene. Fluorescent-labeled probe DNA fragments are added to ask if there are any places on the microarray where the probe strands can match and bind.” [1]

I also found that genetic tests for a wide array of disorders, not just cancer, are already widely used. For instance, newborn babies are commonly screened for a variety of disorders with genetic tests.

There are three different genetic test methods:

1. Chromosome test – detect changes to whole chromosomes.
2. DNA test – examine short stretches of DNA within genes.
3. Protein test – look for protein products of genes.

[http://www.cancer.gov/cancertopics/understandingcancer/genetesting/Slide18]

The only downside to genetic testing is that they find mutations, not the disease itself.
For instance, having an altered gene may increase your chances of getting the disease, but that does not mean that you absolutely, positively WILL develop that disease. It is entirely possible that you will live the rest of your life without ever developing that disease, while someone with a non-altered gene does develop it.
If all I did was confuse you more, this slide may help.

All my questions had been answered.
Since alcohol is banned in the dorms, I celebrated by slamming back a glass of Ocean Spray’s Cran-Grape juice and went to bed.


{For the original slideshow by the National Cancer Institute (where I got this information), click here.}

[1] National Cancer Institute website.