The activating point mutation of the BRAF gene, BRAF T1799A , is the most common and specific genetic alteration in adult papillary thyroid carcinoma (PTC) and a possible marker of malignant potential of PTC. We have applied the PCR-RFLP method using fine-needle aspiration biopsy samples not only to our clinical practice but also to the international medical assistance effort around the Semipalatinsk Nuclear Testing Site in Kazakhstan. Seventy-seven cases (100 nodules) from Japan and 131 cases

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... 137 nodules) from Kazakhstan were examined. There were 14 Japanese and 76 Kazakhstani cases of cytological malignant tumors from the examined samples. We detected 12 (85.7% of PTC) and 19 (25% of PTC) cases with BRAF T1799A among the Japanese and Kazakhstani cases, respectively. Of these cases, we found mutations in one cytologically "suspicious" case and even in two pathologically "benign" cases (after surgery in Kazakhstan). All of the BRAF mutation-positive cases, including those three, were confirmed as PTC by careful pathological examination, including immunohistochemical analysis. In summary, our PCR-RFLP method for BRAF T1799A detection using FNAB samples is useful not only for preoperative diagnosis of PTC but also as a complementary diagnostic tool for accurate pathological diagnosis, even after surgery.