CD44v6 expression in non-anaplastic thyroid carcinoma: characterization of candidates for targeted therapy.

BACKGROUND: CD44v6 is a membranous antigen upregulated in solid tumors and a promising molecular radiotherapy target, especially in anaplastic thyroid carcinoma (ATC). A Phase 1 trial recently launched to evaluate the lutetium-labeled anti-CD44v6 antibody [(1)⁷⁷Lu]Lu-DOTA-AKIR001 in CD44v6-positive solid tumors. Given limited data in non-ATC, we assessed CD44v6 immunoreactivity in tumors that may progress to a radioiodine-refractory state. MATERIALS AND METHODS: An exploratory cohort of 33 tumors (30 papillary thyroid carcinomas [PTCs], 3 poorly differentiated thyroid carcinomas [PDTCs]) was screened using the VFF-7 antibody, supported by detailed iodine concentration, genetic, and RNA sequencing data. A validation cohort of 40 oncocytic thyroid carcinomas (OTCs), 28 additional PDTCs, and one differentiated high-grade thyroid carcinoma was also screened using two antibody clones, VFF-7 and VFF-18. RESULTS: In the exploratory cohort, 10 of 33 tumors (30%) showed focal or diffuse CD44v6 expression, while the rest were negative. Among OTCs in the validation cohort, 15 of 40 (38%) were partially or diffusely positive, and in PDTCs, 14 of 28 (50%) showed focal or diffuse staining. The VFF-7 and VFF-18 clones produced similar patterns. CONCLUSIONS: Substantial subsets of non-ATCs express CD44v6, indicating that some patients may be candidates for [(1)⁷⁷Lu]Lu-DOTA-AKIR001 radiotherapy, particularly when conventional treatments are exhausted.