A single mutation probably causes about two thirds of all cases of papillary thyroid cancer, according to an article in the April 16th issue of the Journal of the National Cancer Institute.

The American researchers identified the mutation of the BRAF gene in 68 percent (24 of 35 samples) of papillary thyroid cancer tumors. Papillary cancer accounts for about 75 percent of all thyroid cancer cases and occurs mostly in women.

"Until now, there have been no other major genetic events identified for common thyroid cancers," said David Sidransky, M.D., senior author of the study. "Our goal is to find better diagnostics and drug therapies designed to target the effects of this mutation."

The change is a single-base mutation, with thymine switched to adenine, in a DNA sequence of more than 2000 nucleotides. The mutation results in gene overexpression, and ultimately it causes carcinogenesis.

"Though most thyroid cancers can be cured by surgery and radioactive iodine treatments, it remains difficult to distinguish benign thyroid disease from cancer," said Sidransky. "Improvements in diagnostic tests and treatments using what we know about the BRAF mutation could speed up diagnosis and help patients survive advanced disease."

Clinical trials for patients with papillary thyroid cancer that has not responded to surgery and radioactive iodine therapy are being planned.

The researchers screened for the BRAF mutation in other cancers and other thyroid tumors. For example, 6 of 9 (66 percent) thyroid cancer cell lines tested positive for the BRAF mutation. No mutations were found in biopsies taken from 20 benign thyroid conditions and other types of thyroid cancer such as follicular, medullary, and Hurthle cell cancer. They found a small percentage of mutation-positive cells in lung and head and neck cancers. A team at another research center has recently found the same mutation in the BRAF gene in approximately 80 percent of melanomas and some colon cancers.