Treatment of Floor of the Mouth Squamous Cell Carcinomas

Primary Site:
- The need for aggressive treatment of floor of mouth carcinomas:
  - Is well recognized
- Surgical resection with a 1 cm margin should be achieved:
  - If surgery is the preferred treatment modality
- Even in the best surgeon’s hands:
  - Positive or close margins may be seen in up to 47% of resections:
    - Despite the use of intra-operative frozen section:
      - Many floor of mouth tumors are infiltrative with indistinct edges:
        
        Possibly explaining the high incidence of positive margins
    - Further resection is advocated if margins are positive
  - Although 1 cm margins are considered by most surgeons to be adequate:
    - Extended 2 cm margins have been advocated by some
- The early extension of floor of mouth tumors into the tongue or mandible:
  - Is demonstrated by the fact that many patients require marginal (rim) or segmental resection of the mandible
- Surgical resection of the floor of mouth in the majority of circumstances:
  - Will involve resection of part of the submandibular ducts:
    - Typically, the ducts will be resected at the resection margin, well away from their orifice:
      - However in smaller resections at least 3 mm length of duct proximal to the orifice:
        
        Should be taken to ensure surgical clearance of carcinoma or dysplasia that may extend along the duct
      - Management of the submandibular ducts is of great importance if a neck dissection is not being conducted with consequent removal of the submandibular gland:
        
        Stricture of the duct in the presence of a functioning gland:
        
        May give rise to obstructive symptoms of the gland and difficulty in differentiating the potential submandibular gland swelling from cervical disease
    - The ducts should be transected obliquely to minimize stricture formation and repositioned at the margin of resection, ideally being stented
    - Alternatively, the ducts may be found proximal to the resection margin:
      - A longitudinal incision made and the duct ‘marsupialized’ to the floor of mouth mucosa:
        
        Uninvolved branches of the lingual nerve should be identified and preserved
- Small resections:
  - May be left to heal by secondary intention or a split thickness skin graft applied
- A more substantial reconstruction may be achieved using local nasolabial or facial artery musculomucosal flaps:
  - However an edentulous segment is required when using both of these flaps to accommodate their pedicle
- If a neck dissection is required and surgical facilities allow;
  - Microvascular reconstruction provides a far more flexible reconstructive option, without necessarily prolonging operative time if a two team approach is adopted

The radial free forearm flap is an ideal reconstructive option for floor of mouth defects:
- Easily being converted to a composite flap if segmental resection of an edentulous mandible is required
Prefabricated fasciomucosal free flaps have been described in oral reconstruction:
- However their role in oncological reconstruction is questioned
The fibula osteocutaneous flap provides superior reconstruction if a segmental resection is anticipated in a dentate patient:
- Although like the composite radial free flap:
  - Flexibility of the skin paddle is limited
The scapula osteocutaneous flap:
- With two skin paddles, or one skin paddle and muscle left to mucosalize:
  - Provides an excellent reconstruction of large defects involving mucosa, bone and external skin
Radiotherapy techniques (brachytherapy or external beam):
- For T1 / T2 primaries have been shown to provide results similar to surgery
- The proximity of the floor of the mouth to the mandible:
  - Is of concern when using brachytherapy:
    - Since up to 8.5% of patients treated with this modality require segmental resection of the mandible:
      - Due to osteoradionecrosis within 10 years
- Several units have described a change in practice from brachytherapy to surgery:
  - As the primary treatment modality due to the risk of complications
- T3 / T4 lesions:
  - Are best treated with surgery and postoperative radiotherapy
Management of the Neck in Floor of the Mouth SCC:
- Regional spread of disease in floor of mouth carcinomas is usually to the ipsilateral level I to III lymph nodes:
  - Involvement of multiple levels not being unusual
- Lesions towards the midline:
  - May spread to both sides of the neck:
    - Hence bilateral neck dissections should be considered
- The presence of lingual lymph nodes:
  - Has raised the concept of in-continuity neck dissection in an attempt to reduce local recurrence and improve survival:
    - Resection of the tumor accompanied with the complete clearance of the floor of the mouth, preserving mylohyoid, hyoglossus and genioglossus if possible, so clearing the lingual lymph nodes would seem an acceptable method of managing lingual lymph nodes
- The decision to conduct an elective neck dissection has been related to tumor size or depth of invasion:
  - Lesions that are T2 or greater:
    - Should have an elective I to III / IV selective neck dissection:
      - Although elective neck dissections have been advocated for T1 lesions
- Tumor thickness of 4 mm is often used as a ‘generic’ critical thickness, greater than which an elective neck dissection is indicated:
  - Since the risk of occult metastasis is greater than 20%:
    - It has been demonstrated that the risk of cervical metastasis of floor of mouth tumors exceeds 20% in tumors as thin as 1.5 mm to 2 mm:
      - Using a thickness of 1.5 mm may result in up to 32% of patients requiring END based on thickness criteria
The indications for postoperative radiotherapy to the loco-regional area are similar to other sites:
- Notably two or more involved nodes in the neck
- Extracapsular spread
- Positive margins
- Stage III / IV disease
Postoperative radiation therapy (PORT):
- The beneficial role of PORT in selected patients with floor of mouth carcinoma has been demonstrated
Recurrence:
- Recurrence rates for floor of mouth carcinoma are 26% to 55%:
  - Usually within the first two years
- Factors that influence recurrence include:
  - Tumor size
  - Margin status
  - Tumor thickness
  - Advanced nodal disease
Prognosis
- Overall five-year survival for floor of mouth carcinoma:
  - Is 52% to 76%
- Factors that potentially influence survival include:
  - Nodal status
  - Thickness
  - Margin status
  - Recurrence