Papillary thyroid microcarcinoma with fatal outcome: evidence of tumor progression in lymph node metastases: Report of 3 cases, with morphological and molecular analysis.

Papillary thyroid microcarcinoma generally carries an excellent prognosis, and fatal cases are becoming increasingly rare. Their pathologic and molecular features, however, remain largely unknown. We describe 3 cases of papillary thyroid microcarcinoma that, despite surgical and radioiodine treatment, recurred, metastasized, and eventually caused the death of the patients. In addition to morphology, immunohistochemical (cyclin D1 and p53) and molecular analyses (BRAF [v-raf Murine sarcoma viral oncogene homolog B1], KRAS [V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog], HRAS [v-Ha-ras Harvey rat sarcoma viral oncogene homolog], NRAS [neuroblastoma RAS viral oncogene homolog], and PIK3CA [phosphoinositide-3-kinase, catalytic, alpha polypeptide]) were performed. Interestingly, all 3 cases presented with massive lymph node metastases that showed morphological evidence of "tumor progression" (tall cell features, poorly differentiated areas, and high-grade cytologic features). Cyclin D1 was consistently immunoreactive in both primary and metastatic site, whereas p53 was negative. BRAF V600E was absent in both sites, and KRAS, HRAS, NRAS, and PIK3CA were consistently wild type. These data suggest that, in cases of metastatic papillary thyroid microcarcinoma, an accurate morphologic analysis of the metastatic deposits could contribute to a more accurate prediction of tumor behavior.