The metabolic boundary at the invasive front of head and neck squamous cell carcinoma: a working model

Local recurrence after R0 resection remains a clinically important problem in head and neck squamous cell carcinoma (HNSCC), even when routine histology identifies no tumor at the surgical margin. Field cancerization, molecular margins, tumor budding, partial epithelial–mesenchymal transition (p-EMT) and invasive-front biology each explain part of this risk, but none defines a spatially resolved metabolic state. In this narrative review, based on searches of PubMed, Web of Science and Embase to 17 October 2026, we examine mitochondrial, lipid, stromal and immune remodeling at the tumor-bearing invasive front, and we separate the published leading-edge multicellular ecosystem (LEMCE) from the metabolic boundary proposed here. LEMCE is a mechanistic model of the tumor-bearing leading edge; the metabolic boundary is a derivative framework asking whether a reproducible metabolic–lipid–cellular signal can be measured at pre-specified spatial coordinates and whether a spatial transition in that signal can be located. The minimum identifiable unit (MIU) is an author-proposed measurement construct, not a validated biological unit, and a positive region is not a boundary. Direct human spatial evidence comes from tumor-bearing leading-edge tissue and from small discovery cohorts whose reported metabolic direction is not uniform. Within the searches performed, we identified no HNSCC study that profiled histologically negative R0 near-margin tissue for the program proposed here. We therefore present the metabolic boundary as a falsifiable research framework rather than a clinical margin criterion, and we distinguish two separable questions: whether the spatial state exists and is reproducible, and whether it adds prognostic information.