Abandoning node dissection for desmoplasia-negative encapsulated unifocal sporadic medullary thyroid cancer.

Background: Predictive criteria to determine the absence of node metastases from thyroid specimens are scarce for sporadic medullary thyroid cancer.

Methods: Histopathologic stratification of patients with unifocal sporadic medullary thyroid cancer ≤25 mm with ≥10 neck nodes at thyroidectomy to evaluate the suitability of desmoplasia (7 increments) and tumor capsule integrity (5 decrements) for intraoperative prediction of node metastasis in unifocal sporadic medullary thyroid cancer.

Results: Paraffin-embedded thyroid specimens were available for 139 eligible patients. Significant (P < .001) associations were found between increasing desmoplasia and decreasing tumor capsule integrity and nodal disease (from 0 to 79% and 0 to 62%); the number of node metastases (medians, from 0 to 3 and 0 to 2 nodes); and biochemical cure (from 100 to 36% and 100 to 58%). Desmoplasia (low-moderate to high, with fibrosis >10%) and breach of the tumor capsule (>3 extensions; 1 extension >3 mm in width; or diffuse growth without tumor capsule) yielded excellent sensitivity and negative predictive value (100%), with moderate specificity (57 and 48%) and positive predictive value (50 and 46%). In retrospect, node dissection proved unnecessary in 55 (57%) and 47 (48%) patients who harbored desmoplasia-negative and encapsulated tumors. When available frozen sections were histopathologically compared with matching paraffin-embedded thyroid tumor specimens, concordance was 98% (53 of 54 pairs): 1 of 7 upgrades changed the diagnosis to desmoplasia, whereas 1 of 3 downgrades shifted the diagnosis of tumor capsule breach from "present" to "absent."

Conclusions: Patients with desmoplasia-negative encapsulated sporadic medullary thyroid cancer may forgo node dissection at specialist centers.