Accuracy Matters When It Comes to Diagnosing Cancer

Breast cancer has been a part of Katie King Mahan’s family. Her mother, grandmother and great-grandmother survived breast cancer—each of them having dealt with the disease at a relatively young age.

Due to her family’s history of breast cancer, Mahan, a stay-at-home mom and yoga instructor in Marblehead, Mass., was considered at high-risk of developing the disease. “My mom was 29 was she was diagnosed,” Mahan says. “As my 30th birthday approached, I recognized that I would do whatever it took not to be next.”

For Mahan, that meant getting tested for genetic mutations in the BRCA1 and BRCA2 genes. Mutations in either or both genes are known to put women at significantly higher risk of developing hereditary breast and ovarian cancer than women who do not have the mutation. Ideally, genetic testing should start with a family member who has breast or ovarian cancer since unaffected blood relatives may not share the same gene, but that is not always possible.

In fact, as many as 45 to 65 percent of women with BRCA mutations will develop breast cancer, compared with 12 percent of women who do not have the mutations. Similarly, 11 to 39 percent of women who inherit either or both of the BRCA mutations will develop ovarian cancer, compared with 1.4 percent of women without the mutations.

After testing positively for the mutation at age 32, Mahan decided to have both breasts surgically removed.

“For me, it was an obvious choice,” Mahan says of the procedure, which is also called a bilateral prophylactic mastectomy. “I have a husband and child who need me.”

In electing to have the surgery, Mahan reduced her risk of developing breast cancer from as high as 87 percent to less than 1 percent. She also plans to have her ovaries removed within the next five years—a procedure that will reduce her risk of developing ovarian cancer before the age of 70 by as much as 90 percent.

For me, it was an obvious choice. I have a husband and child who need me.

Mahan’s experience demonstrates the potential of using biomarkers to predict cancer risk. A biomarker is a characteristic—in Mahan’s case, a protein that indicates a mutated BRCA2 gene—that may signal, among other things, the presence of disease.

As new molecular technologies have been developed that allow for the examination of thousands of genes and other molecular characteristics, patterns of gene activity, changes to DNA and chromosomal abnormalities have also begun to be used as biomarkers. Many of these biomarkers are used, much like the BRCA genes, for risk stratification—that is, to determine a person’s risk for developing cancer. In fact, risk-stratification biomarkers are now being used for brain, cervical, colorectal, esophageal, liver and pancreatic cancers. Some biomarkers are inherited (particularly those associated with a high risk of developing certain cancers—these can be used to determine the benefits of prophylactic or risk-reducing treatments), while other markers are acquired (only seen in the tumor and not passed on to children—these can be used to estimate the risk of recurrence or to help choose the best therapy).

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