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Year in review: Cancer genetics grows up

Reporter: Evelina Cohn, PhD

Personalized genomics is the next research in cancer. However not all the mutations found in this disease are targeted equally by the researchers.

“Genetics is changing oncology for the good,” says Benjamin Kipp, an expert in clinical genetics at the Mayo Clinic in Rochester, Minn. “But overinterpretation can harm the patient.”

Genetic profile of tumors offers opportunities for both cancer diagnostics and treatment. For example, bowel cancer tumors with mutations in the KRAS gene respond poorly to the drug Cetuximab, while the drug Vemurafenib works only in melanomas that have a particular mutation in BRAF gene. But such genetic testing can be misleading if it isn’t conducted alongside tests of healthy cells from the same person, says oncologist Victor Velculescu of the Johns Hopkins University School of Medicine. He led a vast analysis comparing the genetic profiles of tumors and normal tissue of more than 800 cancer patients and found that nearly two-thirds of mutations in the studied tumors — many of which might be used to guide treatment — also showed up in patients’ healthy tissues . Thus, there are many “false positive” mutations that appear to contribute to cancer but in reality they are showing up elsewhere in an individual’s health tissue. Sampling both tumor and healthy tissues might provide a way to sort out truly cancerous mutations, the scientists report.

A team of researchers in Baltimore tested tumor tissue and healthy tissue from 815 patients who had various cancers. Using only the tumor analysis, the tests spotted an average of 382 mutations per case that appeared associated with cancer. But nearly two-thirds of these variations, on average, also showed up in healthy tissues, suggesting that they weren’t driving the cancer, the authors report in the April 15 Science Translational Medicine.
For those patients, the mutations were probably just benign variants unrelated to the cancer. Analyzing healthy tissue can also reveal whether mutations found in tumors are heritable or not, Velculescu says, which is important for deciding whether a cancer patient’s family should receive genetic counseling.

Even mutation that have been linked to the cancer not always manifest as cancer making this interpretation even worse. A study published in May examining eyelid skin discovered numerous cancer-associated mutations in normal, healthy patches of the skin. Researchers had previously thought that the types of mutations that fuel tumor growth were rare and happened just before a cell becomes cancerous. But a study of the eyelids of four people who don’t have cancer reveals that such mutations “are staggeringly common in normal skin,” says Philip Jones, a clinical scientist at the University of Cambridge. Thus, Jones and his colleagues collected 234 skin samples from four people ages 55 to 73 who had plastic surgery to correct droopy eyelids. DNA sequencing showed that about 20 percent of the skin cells had mutations in the NOTCH1 gene, the team reports in the May 22 Science. When mutated, that gene is a driving force in some cancers, including skin cancers called squamous cell carcinomas.

As genetic testing of tumors becomes more widespread, best practices will emerge, as will a better understanding of the disease. “We are trying to change the way we look at cancer,” says Sameek Roychowdhury, a medical oncologist at the Ohio State University Comprehensive Cancer Center in Columbus. “But we are just seeing the tip of the iceberg.”

Conclusion: We have to be really careful when are making interpretation of mutated genes that may cause cancer and identify those mutations in both healthy and cancer tissues as well as find the expression of those genes that may lead to cancer, being said that only cancer mutations that are expressed may have an importance in cancer appearance.

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