Papillary thyroid carcinomas have mutations
in the BRAF gene that can be detected in biopsy specimens
(November 2004)
The background of the study. Fine-needle aspiration
biopsy usually provides sufficient tissue to distinguish between
benign and malignant thyroid nodules on the basis of cytologic evaluation
of the biopsy. However, some biopsies are not diagnostic. Some papillary
thyroid carcinomas have a mutation in the BRAF gene, which codes
for B-Raf kinase, an enzyme in a signaling pathway involved in cell
differentiation and growth. In this study the mutation was sought
in biopsy specimens.
How the study was done. Biopsies of thyroid nodules
and thyroid tissue from 45 patients were analyzed for BRAF mutations
by DNA sequencing and a colorimetric test that specifically detected
the BRAF mutation.
The results of the study. Among the 40 patients
who underwent surgery, 26 had a thyroid nodule with a nondiagnostic
biopsy, 10 had a thyroid nodule with a biopsy indicating papillary
carcinoma, 3 had a nodule with a biopsy diagnosis of benign nodule,
and 1 had no biopsy. The final pathologic diagnosis was papillary
carcinoma in 16 patients, follicular carcinoma in 6, benign adenoma
or hyperplastic nodule in 17, and metastatic kidney carcinoma in
1. Five patients did not have surgery; the biopsy revealed benign
thyroid cells in 4 and was nondiagnostic in 1.
The colorimetric analysis of the biopsy specimens revealed the
BRAF mutation in 8 of the 16 papillary carcinomas (50 percent),
but in none of the benign nodules, the follicular carcinomas, or
the metastatic kidney carcinoma. The result in the nondiagnostic
nodule of the patient not operated on was negative. The results
of the DNA sequencing analysis were similar, except that the mutation
was detected in only six of the papillary carcinomas.
The conclusions of the study. BRAF gene mutations
can be detected in biopsy specimens of some papillary carcinomas,
but are not found in follicular carcinomas or benign thyroid nodules.
The original article. Xing M, Tufano RP, Tufaro
AP, Basaria S, Ewertz M, Rosenbaum E, Byrne PJ, Wang J, Sidransky
D, Ladenson PW. Detection of BRAF mutation on fine needle aspiration
biopsy specimens: a new diagnostic tool for papillary thyroid cancer.
J Clin Endocrinol Metab 2004;89:2867-72.
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