Floor of mouth cancers occur with a frequency similar to that for tongue cancer. Early spread to adjacent areas (gingiva and periosteum of the mandible) is common. The periosteum is a natural barrier to spread. Fixation of the tongue is a sign of deep invasion. The tumor may extend to or through the myohyoid muscle, which serves as a natural barrier to direct spread below the hyoid bone. Lymph node metastases at presentation are seen in approximately 40% of patients and an additional 20% have occult lymphatic metastases. The occult metastatic rate increases with the T stage of the primary: T2 tumors have a 40% and T3 tumors a 70% occult metastasis rate.

First-echelon nodes of lymphatic drainage include the submandibular and jugulodigastric lymph nodes (levels I and II). Submental node involvement is unusual. Evaluation for early mandibular involvement is facilitated by palpation since fixation to the mandible indicates periosteal involvement and direct bone invasion is present in 50% to 60% of such tumors.

Small cancers (T1, T2) are generally treated effectively by wide resection. Little morbidity results from surgical resection of superficial lesions. Lateral floor-of-mouth tumors can often be resected transorally and the resection defect closed with the advancement of adjacent mucosa, skin grafts, or secondary intention. Early cancers involving the mandible are best treated surgically because bone involvement compromises radiation efficacy. Surgery remains the mainstay of treatment for early floor-of-mouth malignancies, achieving excellent functional and curative results.

Radiation therapy for small floor-of-mouth cancers usually involves combinations of external radiation and brachytherapy. Decision making concerning primary therapy takes into consideration the expected functional result, the management of the neck nodes, and the risk of osteoradionecrosis. Radiotherapy for moderate-size (T2) anterior floor-of-mouth lesions and small or deeply invasive cancers must also include treating bilateral first-echelon lymph nodes. Rates of occult nodal metastases range from 30% to 40%.

More advanced floor-of-mouth cancers (T3, T4) are generally treated with resection combined with postoperative radiation of the primary and regional nodes. These resections require a transcervical approach and are combined with neck dissection and mandibular resections as needed. Again, mandibular continuity-sparing procedures with cortectomies can often be employed. In these instances, we have found fasciocutaneous flaps to offer excellent floor-of-mouth and tongue reconstructive potential. Large surgical defects are reconstructed with skin grafts, local flaps, myocutaneous pedicled regional flaps, and frequently free-tissue transfers. Mandibular reconstruction for segmental defects is performed primarily with composite free-tissue transfers.

Doses of radiation therapy for locoregional tumor control are based on actual tumor volume rather than T stage. Interstitial doses of 65 to 75 Gy are recommended for early lesions (1 to 3 cm) if brachytherapy alone is used, or external beam radiation of 50 Gy combined with 25 to 30 Gy of interstitial radiation. Postoperative doses are given by external radiation only at doses of 65 Gy over 6 to 7 weeks, or preoperative doses of 50 Gy over 6 weeks. No significant differences in overall survival rates have been shown when comparing preoperative and postoperative radiation regimens.

Treatment results are influenced by the size of the primary tumor, presence of lymph node metastases, degree of mandibular involvement, and adequacy of resection. The 5-year survival rates for localized stages I and II carcinomas of the floor of mouth range from 60% to 80% (

Table 90-7). Cancers that cross the midline or involve the tongue or the mandible are associated with 5-year survival rates of 50% to 60%. Survival rates for more advanced lesions (stages III and IV) are less than 50%. Lymph node metastases decrease survival rates to approximately 25%. The major advantage of combined treatment (radiation and surgery) in these patients is improved control of ipsilateral and contralateral neck disease. Because rates of occult nodal disease are high in advanced primary lesions, elective treatment of the neck with radiation or bilateral neck dissections is indicated. Recurrence in the untreated, clinically negative neck is the most frequent site of failure in patients treated only with surgery.

The debate over performing elective neck dissection versus irradiation remains unresolved. If adequate primary tumor margins are uncertain or if multiple histologically positive lymph node metastases are detected, postoperative radiation to the ipsilateral and contralateral neck is administered. The development of second primary cancers is a major cause of morbidity and death. Fu and colleagues reported that 55 of 153 (36%) patients developed second primaries, of whom 30 died of their second cancer. Distant metastases occur in 10 to 15% of patients.