Answer: Papillary thyroid carcinoma

Histology: The tumor is a well circumscribed nodule that appears distinct from the remainder of the thyroid. On low magnification, the tissue in the nodule appear somewhat paler than the surrounding normal thyroid. On higher magnification the nuclei are noted to be overlapping and crowded, large, and optically clear. Nuclear grooves are also observed. Rare rudimentary papillary formations can be seen in some follicles.

Discussion: The infiltrate of lymphocytes with prominent germinal center formation is typical of Hashimoto’s thyroiditis. A well circumscribed nodule seen adjacent to the thyroid gland with Hashimoto’s thyroiditis shows features for follicular variant of papillary thyroid cancer. Those features include enlargement of the nuclei with clearing of the chromatin. In addition, the nuclei can be seen overlapping each other, along with nuclear grooves. These features are helpful in distinguishing this nodule from follicular adenoma and graves disease, which would have more benign appearing nuclei.

Patients with Hashimoto’s thyroiditis have an increased risk for papillary carcinoma of the thyroid. These tumors are associated with the RET oncogene. The overall prognosis for patients with papillary cancer is excellent. Extra-thyroid extension into soft tissues of the neck is seen in approximately twenty five percent of patients. Involvement of cervical lymph nodes is very common and does not adversely affect the prognosis. Factors that are associated with a worse prognosis are age greater than forty years, extra thyroid extension, large tumor size, multicentricity, distant metastasis, and presence of anaplastic foci.