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C04 covers primary malignant neoplasms of the floor of the mouth, an oral cavity site beneath the mobile tongue. Subsites include the anterior floor, lateral floor, overlapping sites, and an unspecified floor-of-mouth location. Tobacco and heavy alcohol exposure are major risk factors.
Common Histologies
- Squamous cell carcinoma accounts for most cases.
- Less common tumors include minor salivary gland carcinomas and other rare epithelial malignancies.
- HPV-associated biology is less characteristic than in oropharyngeal squamous cell carcinoma; p16 positivity alone should not be interpreted using HPV-mediated oropharyngeal staging.
Common Symptoms
- Persistent oral ulcer (K12.0), plaque (K03.6), mass (K13.70), or induration (K13.79)
- Floor-of-mouth pain (R07.0), bleeding (R58), or tenderness (R68.89)
- Difficulty chewing (R13.11), swallowing (R13.10), speaking (R47.9), or moving the tongue (R25.8)
- Referred ear pain (H92.09)
- Loose teeth or mandibular symptoms with advanced local invasion (C41.1)
- Neck mass from regional lymph-node involvement (R22.1)
Diagnosis
Evaluation generally includes complete oral cavity and neck examination, assessment of tongue mobility, and tissue biopsy. Contrast-enhanced CT or MRI helps define deep soft-tissue, mandibular, and nodal involvement. Chest imaging and, in selected advanced cases, FDG PET/CT may be used to evaluate distant disease or synchronous malignancy.
Staging
Floor-of-mouth cancers are staged as oral cavity cancers. Staging considers:
- Primary tumor size and depth of invasion
- Extension into adjacent oral cavity structures or mandible
- Cervical lymph-node burden and extranodal extension
- Distant metastasis
Regional spread commonly involves submental, submandibular, and upper cervical lymph nodes.
Molecular Markers
Routine management is primarily driven by anatomy, histology, and stage rather than a single site-specific biomarker. Biomarker testing may be appropriate in recurrent or metastatic disease, including PD-L1 assessment and broader molecular profiling when results could guide systemic therapy.
Common Treatments
- Surgical resection is commonly used for resectable disease, often with evaluation or dissection of the cervical lymph nodes.
- Reconstruction may be required to preserve swallowing, speech, tongue mobility, and mandibular function.
- Postoperative radiation is considered for adverse pathologic features.
- Concurrent chemoradiation may be used for high-risk findings such as positive margins or extranodal extension.
- Definitive radiation or chemoradiation may be appropriate in selected nonsurgical cases.
- Recurrent or metastatic disease may be treated with immunotherapy, chemotherapy, targeted systemic therapy when actionable, radiation, surgery, or symptom-directed care.
Scope Note
C04 identifies the primary anatomic site as the floor of the mouth and may further distinguish anterior, lateral, overlapping, or unspecified subsites. It does not encode histologic type, grade, tumor stage, depth of invasion, nodal status, molecular findings, or treatment status. It is not a code family for secondary/metastatic involvement of the floor of the mouth; metastases and other secondary malignancies are classified separately. Associated alcohol-use disorders and history of tobacco dependence may be captured with additional codes when documented.