Dying tumor cells as a driver of tumor repopulation after insufficient thermal ablation of papillary thyroid carcinoma.

e18046 Background: Although high-quality clinical evidence remains limited, the use of thermal ablation for papillary thyroid carcinoma (PTC) is increasing. Emerging data suggest that thermal ablation may accelerate tumor progression in a subset of patients, yet the underlying biological mechanisms are poorly understood. This study aimed to elucidate the clinical features and underlying mechanisms of accelerated tumor relapse after thermal ablation. Methods: Clinical pathological features of post-ablation surgical specimens were analyzed and Xenium in situ spatial transcriptomics was conducted. In vitro and in vivo models were established to simulate accelerated tumor repopulation following insufficient thermal ablation and to investigate the underlying mechanisms. Time-lapse imaging and RNA sequencing were performed to characterize how heat-induced dying cells influence the behavior of surviving cells. Quantitative PCR, Western blotting, immunohistochemistry (IHC), and flow cytometry (FACS) were used to validate candidate molecular mechanisms, and enChIP-MS was applied to identify upstream regulatory factors. Results: Compared with patients receiving initial surgical treatment, patients receiving thermal ablation present with significant higher proliferation index (Ki-67% 8% vs 1%), and the phenomenon is significantly presented in area close to the ablative zone. Mechanistically, heat-induced dying cells promoted the repopulation of surviving cells in a contact-dependent manner after insufficient thermal ablation, and this effect was not attributable to a single mode of cell death. Dying cells upregulated DLL4, which activated Notch signaling in surviving cells and drove their proliferation. Moreover, anti-DLL4 antibody treatment effectively attenuated the dying cell–mediated proliferative effect both in vitro and in vivo. Upstream analysis revealed that HNRNPU was enriched at the DLL4 promoter after heat treatment, facilitating DLL4 transcription and amplifying its expression. Conclusions: Insufficient thermal ablation significantly accelerate tumor progression. Heat-induced dying cells play a vital role in the process via activation of the DLL4–Notch pathway. As a relative less malignant tumor, the use of treatment without strong clinical evidence and underdetermined risks should be with caution.