LQHS2605 - CMLE - Evaluation of Bone Invasion in Oral Squamous Cell Carcinoma-Evaluation of Bone Invasion in Oral Squamous Cell Carcinoma

Evaluation of Bone Invasion in Oral Squamous Cell Carcinoma

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This document is a histology continuing education exercise focused on accurate processing of mandibular bone specimens in oral squamous cell carcinoma (OSCC) to support correct pathologic staging, especially assessment of medullary bone invasion. It explains that, under AJCC 8th edition criteria, tumor penetration through cortical bone upstages OSCC to pT4a regardless of tumor size, while superficial cortical erosion does not. Because staging influences treatment decisions, careful specimen handling and processing are emphasized as essential to diagnostic accuracy.<br /><br />A case is presented involving a 54-year-old man with a gingival OSCC who underwent segmental mandibulectomy. Grossly, the tumor approached and appeared to erode bone near tooth sockets. During processing and microscopic review, definitive categorization of bone involvement was difficult due to technical and anatomic challenges: bone fragmentation at multiple steps (grossing, decalcification, sectioning), an ill-defined cortico-medullary junction (especially where cortical bone is naturally thin around tooth sockets), suboptimal sampling of the tumor–bone interface, and the impact of decalcification on H&E and ancillary test quality. These issues can create artifacts and interobserver variability, complicating determination of whether tumor truly breached cortex into marrow spaces.<br /><br />The document reviews decalcification principles and tradeoffs. Under-decalcification leads to difficult cutting, tissue cracking, and slide loss; over-decalcification can damage cytology and diminish nuclear detail and immunohistochemical performance, particularly if fixation is inadequate. Strong acids decalcify quickly but can degrade nucleic acids and compromise molecular testing; EDTA is slower but better preserves nucleic acids. Because some FDA-approved biomarker IHC assays may not be validated for decalcified tissue, the recommended approach is to decalcify only what is necessary for diagnosis while preserving undecalcified tumor for ancillary studies when anticipated.<br /><br />In the case, deeper levels and additional sampling ultimately demonstrated tumor nests in trabecular bone and marrow spaces, confirming medullary invasion and resulting in final staging of pT4a N2b, followed by adjuvant chemoradiotherapy and disease-free follow-up at 12 months.

Keywords

oral squamous cell carcinoma (OSCC)

mandibular bone specimen processing

histology continuing education

AJCC 8th edition staging

medullary bone invasion

cortical bone erosion vs penetration

segmental mandibulectomy

decalcification (EDTA vs strong acids)

tumor–bone interface sampling

pT4a upstaging