Positive surgical margins (PSMs) are a major predictor of recurrence in thyroid cancer; however, their intraoperative detection remains challenging, particularly for microscopic PSMs. This study aimed to demonstrate that a sprayable pH-sensitive near-infrared fluorescent probe (PH10) could specifically and robustly label thyroid tumors in orthotopic mouse models. The pH sensitivity, cytotoxicity, and cellular uptake mechanisms of PH10 were evaluated in papillary thyroid carcinoma (K1) and anaplastic thyroid carcinoma (8505C) cell lines in vitro. Orthotopic thyroid cancer mouse models were then established using both K1 and 8505C cells. In vivo fluorescence following topical spraying of PH10 was quantified after sequential washes to assess tumor-to-background ratios. Fluorescence-guided surgery (FGS) was performed to determine whether PH10 could facilitate complete resection of orthotopically grown thyroid tumors. Complete resection was validated by hematoxylin and eosin histology. PH10 demonstrated low cytotoxicity at clinically relevant concentrations in vitro and showed selective uptake into thyroid cancer cells, predominantly via organic anion transporting polypeptide-mediated transport. Topical spraying of PH10 in orthotopic thyroid cancer mouse models established from K1 and 8505C cell lines generated strong tumor-specific fluorescence. Tumor-to-background ratios were significantly higher than background and remained distinguishable after multiple washes. In both models, PH10 enabled visualization of macroscopic residual tumors and detection of microscopic PSMs, with fluorescence patterns closely corresponding to histologic findings. FGS enabled complete tumor resection, as confirmed by fluorescence and histology. In conclusion, topical application of PH10 provides rapid, tumor-specific fluorescence suitable for identifying PSMs and facilitating complete tumor resection by FGS in thyroid cancer.

Background/Objectives: The majority of thyroid cancer patients are diagnosed with papillary thyroid cancer. A complete R0 resection significantly lowers cancer recurrence risk for high-risk papillary thyroid cancer but can be difficult to achieve because tumor margins are not easily visualized. The purpose of the present narrative review is to describe current work and future directions in fluorescence-guided thyroid cancer surgery. Methods: PubMed and Google Scholar were used to identify 45 articles that focused on fluorescence labeling and imaging of thyroid cancer published through February 2026 using the search terms “thyroid cancer” AND (“fluorescence imaging,” OR “NIR imaging” OR “optical imaging”) OR “fluorescence guided thyroidectomy”. Standalone abstracts and publications not available in English were excluded. Results: 17 fluorescent probes were shown to visualize tumor margins and micrometastases, 3 probes were able to visualize nerves, and 2 probes targeted lymph nodes. Most studies were done using animal models. Two probes (EMI-137, which targets tumors, and bevonescein, which targets nerves) were tested in clinical trials with good safety profiles. Conclusions: Several tumor-targeted fluorophores and optical imaging strategies have shown promise for thyroid cancer localization, margin assessment, lymph node evaluation, and nerve visualization; however, most remain preclinical, and clinical utility will require standardized dosing, imaging thresholds, safety assessment, and outcome-based validation with multicenter clinical trials.