Floor of Mouth Cancer: Early Signs, Staging and Surgical Treatment — A Comprehensive Guide

The floor of mouth (FOM) is the crescent-shaped mucosal region between the lower dental arch of the mandible and the undersurface of the tongue. The submandibular and sublingual salivary gland ducts (Wharton and Bartholin ducts) open here. The lingual nerve, hypoglossal nerve and major lingual vessels run through this plane; tumour invasion can therefore cause neurovascular complications.

FOM cancer accounts for 25-35% of all oral cavity cancers and is the second most common oral subsite after the tongue. Incidence is higher in countries with heavy tobacco and alcohol use including Türkiye. Male-to-female ratio is about 3:1, with peak age 55-70.

Histology: approximately 95% of cases are squamous cell carcinoma (SCC). Rarer types include minor salivary gland carcinomas (adenoid cystic, mucoepidermoid), verrucous carcinoma and occasionally melanoma.

Risk factors: tobacco use is the most powerful factor — every form (waterpipe, pipe, smokeless tobacco) raises risk including secondhand exposure. Alcohol is an independent risk factor synergistic with smoking; >30 g daily alcohol raises risk 6-15-fold. HPV (especially high-risk type 16) is rising globally; HPV-positive tumours occur in younger non-smokers with better prognosis. Poor oral hygiene, chronic mechanical trauma (ill-fitting dentures, broken teeth), nutritional deficiency (especially vitamins A and C), iron-deficiency anaemia (Plummer-Vinson syndrome), xerostomia and immunosuppression are additional factors.

Premalignant lesions: leukoplakia and erythroplakia are clinical precursors. Leukoplakia transforms in 5-15% of cases; erythroplakia in 40-50% — erythroplakia is far more aggressive. Routine biopsy of suspicious premalignant lesions is mandatory. We expand on the clinical framework in our head and neck cancer surgery programme.

Early clinical features: a painless or mildly tender sore beneath the tongue or near the lower dental arch lasting >2-3 weeks, white (leukoplakia) or red (erythroplakia) plaque, small induration, occasional bleeding. Advanced disease: enlarging ulcerative mass, odynophagia, restricted tongue mobility, referred otalgia (via lingual nerve), numbness (lingual or mandibular nerve invasion), trismus (masticator space invasion), voice change, sublingual or submandibular duct involvement, foul breath.

Lymphatic spread is common: midline FOM lesions spread bilaterally to submental (level Ia) and submandibular (level Ib) nodes; lateral lesions spread to ipsilateral submandibular and upper jugular (level II) nodes. At first presentation, 30-50% of patients have palpable or imaging-detectable nodal metastasis.

Diagnostic workup: detailed head and neck examination (bimanual palpation is the gold standard for FOM — one finger intraoral, the other hand on submental/submandibular region). Punch or incisional biopsy of the suspicious lesion. Systematic bilateral palpation of all cervical levels.

Imaging: contrast-enhanced neck MRI is first-line for soft tissue and perineural invasion; CT better delineates mandibular cortex involvement. PET/CT for distant metastasis and second primary screening in T3-T4, N+ disease and aggressive histology. Dental consultation (for pre-radiotherapy extraction needs) is important.

Staging (AJCC 8th edition — oral cavity TNM):

T1: tumour ≤2 cm and depth of invasion ≤5 mm; T2: 2-4 cm or depth 5-10 mm; T3: >4 cm or depth >10 mm; T4a: invasion of mandibular cortex, extrinsic tongue muscles, maxillary sinus or facial skin; T4b: invasion of masticator space, pterygoid plates or skull base.

N: regional nodes. N0: none; N1: ipsilateral single ≤3 cm without extranodal extension (ENE); N2: 3-6 cm or multiple or bilateral; N3: >6 cm or ENE positive. Extranodal extension is an important prognostic factor in modern staging.

M: distant metastasis (lung, bone, liver — advanced cases).

Surgical resection is the cornerstone of FOM cancer treatment. Goal: en-bloc resection with ≥5 mm negative margins. Resection approach is chosen by tumour size, location and depth of invasion:

Transoral approach: small (T1-T2) superficial anterior tumours can be resected via the mouth using CO2 laser or cold-knife techniques. Advantages: cosmetic superiority, no mandibular osteotomy needed, faster recovery.

Pull-through (visor) approach: for midline or moderate-size tumours allowing resection of FOM with tongue, preserving mandibular integrity.

Paramedian mandibulotomy: in larger tumours without mandibular invasion, the mandible is split to improve access and reconstructed with plates and screws after resection.

Segmental mandibulectomy: required for T4a tumours invading mandibular cortex or medulla. Fibula free flap is the gold-standard reconstruction.

Neck dissection: in FOM cancer with midline lesions or depth >4 mm, bilateral elective selective neck dissection (levels I-III) is recommended. Lateral T1-T2 superficial lesions allow ipsilateral selective dissection. N+ disease requires therapeutic modified radical or extended selective dissection. Sentinel lymph node biopsy is emerging as an alternative in selected centres.

Reconstruction is planned by defect size. Small defects: primary closure or local mucosal flap. Medium defects: radial forearm free flap (soft, pliable, foldable) is standard. Large defects involving mandible: fibula osteocutaneous free flap (bone + skin + vessels) is preferred. Preservation of tongue mobility, swallowing and speech is the central reconstructive goal. More detail: oral cavity cancer page.

Adjuvant radiotherapy (RT) indications: positive or close surgical margin (<5 mm), perineural invasion, lymphovascular invasion, multiple positive nodes, T3-T4 stage, poor differentiation. Total dose 60-66 Gy over 6-7 weeks in weekly 5-fraction schedules. Modern IMRT (intensity-modulated RT) spares salivary glands, larynx and spinal cord.

Adjuvant chemoradiotherapy (CRT) indications: extranodal extension positive (ENE+) and/or positive surgical margin. Standard chemotherapy is high-dose cisplatin (100 mg/m² every 3 weeks, 3 cycles) concurrent with RT. In elderly or comorbid patients, weekly low-dose cisplatin (40 mg/m²) or cetuximab is an alternative.

Immunotherapy: in recurrent and metastatic disease, PD-1 inhibitors (pembrolizumab, nivolumab) are important. In high PD-L1 expression, first-line monotherapy; lower expression often combined with chemotherapy.

Multidisciplinary tumour board: surgical oncology, medical oncology, radiation oncology, pathology, radiology, head and neck reconstructive team, dentist, speech-swallow therapist, nutrition specialist and psychosocial support are involved to personalise every case.

Swallow and speech rehabilitation: speech-swallow therapy starts early postoperatively. Dysphagia management includes texture-adjusted diet, postural training, aspiration-prevention techniques. Large resections may need temporary PEG (percutaneous endoscopic gastrostomy) feeding.

Recurrence and follow-up: local recurrence typically within 1-2 years; regional (neck) recurrence within the first 3 years. Year 1-2: head-neck exam every 2-3 months; years 3-5 every 4-6 months; after 5 years annually. Imaging is individualised; high-risk cases get 6-monthly MRI for the first 2 years. Recurrence prompts multidisciplinary review of reoperation, salvage RT and systemic therapy.

Survival: 5-year overall in FOM cancer — Stage I 75-85%, Stage II 65-75%, Stage III 45-55%, Stage IV 25-35%. HPV-positive cases have significantly better prognosis than HPV-negative.

Poor prognostic factors: advanced T stage, nodal positivity (especially with extranodal extension), perineural invasion, lymphovascular invasion, inadequate surgical margin, poor differentiation, continued smoking/alcohol use after treatment, immunosuppression.

Second primary cancer risk: 15-20% of FOM cancer patients develop a second primary head-neck, lung or oesophageal cancer within 5 years — the "field cancerisation" concept. Annual head-neck exam plus lung and oesophageal surveillance is standard.

Prevention: smoking and alcohol cessation are primary protection. Even in diagnosed patients, cessation meaningfully improves treatment outcome and recurrence rates. HPV vaccination (9-valent) prevents HPV-related head-neck cancers in young populations. Good oral hygiene, regular dental follow-up, repair of ill-fitting dentures and broken teeth reduce chronic mechanical trauma. Nutrition — adequate vitamins A and C, iron; fruit- and vegetable-rich diet is protective.

Early screening and awareness: all smoking/alcohol-using patients over 40 should have annual oral examination. Dentists and ENT clinicians should perform routine bimanual FOM examination. Patients are advised: any sore, lump or colour change beneath the tongue lasting >2-3 weeks must not be ignored.

Patient support programmes: psychosocial support, smoking-cessation clinics, nutrition counselling, speech-swallow therapy and family counselling should be offered during treatment. Patient associations and online support groups improve motivation. Related reading: our multidisciplinary tumour board.