Occult Multifocal Papillary Thyroid Microcarcinoma Presenting as a Supraclavicular Mass Containing Anaplastic Thyroid Carcinoma

Importance: There are reports in the literature of anaplastic thyroid carcinoma in cervical lymph nodes with evidence of only papillary carcinoma in the thyroid gland. There have been no cases of this clinical scenario with only papillary microcarcinoma in the thyroid gland. Observations: We describe the case of a 60-year-old man who initially presented with an enlarged right, level 5, supraclavicular lymph node. Initial fine-needle aspiration demonstrated evidence of papillary thyroid carcinoma. The final pathologic finding in the thyroid gland showed only multiple foci of papillary thyroid microcarcinoma. The index neck mass showed evidence of anaplastic thyroid carcinoma. Conclusions and Relevance: This is the first instance in the literature in which anaplastic thyroid carcinoma has appeared in metastatic cervical lymph nodes with only a focus of papillary microcarcinoma in the thyroid gland. With this case, we hope to build awareness of this rare finding.