Influence of bone invasion on outcomes after marginal mandibulectomy in squamous cell carcinoma of the oral cavity.

INTRODUCTION

Marginal mandibulectomy (MM) is indicated for oral cavity squamous cell carcinomas (OCSCC) that abut or minimally erode the mandible without gross invasion. Successful implementation of MM is predicated on accurate patient selection and appropriate adjuvant treatment based on well-known host and tumor characteristics. The incidence of microscopically diagnosed bone involvement in MM specimens and its implications on outcomes have however not been reported in large contemporary series.

PURPOSE

To report the incidence of bone involvement and analyze its influence on oncologic outcomes in selected patients who underwent MM in treatment of OCSCC.

METHOD

A retrospective cohort study was performed on a consecutive series of previously untreated patients requiring MM, at a tertiary care cancer center, between 1985 and 2012 (n = 326). The median age was 64 years and 59% were male. The majority of patients (67%) had a primary tumor of the floor of the mouth or lower alveolus, 80% were clinically staged T1-2, and 31% were clinically N+. Postoperative radiation (PORT) was used in 27% and chemoradiation (POCTRT) in 8% of patients who had microscopic bone invasion. The median follow up period was 55 months and endpoints of interest were local and regional recurrence free (LRFS and RRFS) and disease specific (DSS) survival.

RESULTS

Microscopic bone invasion was present in 15% of patients (n = 49). Among these, cortical invasion was present in 32, medullary in 13, and it was not specified in 4. Eight patients had microscopic positive bone margins. Positive bone margins were associated with medullary bone involvement (p < 0.001), floor of mouth and buccal mucosa primary site (p = 0.03), and positive soft tissue margins (p = 0.06). LRFS and DSS were similar in patients without versus with bone invasion (62.8% vs 79.7% and 76.2% vs 66% respectively, p = NS). LRFS were similar in patients with microscopic positive versus negative bone margins, as long as postoperative adjuvant treatment was administered.

CONCLUSION

Microscopic bone involvement does not adversely influence outcomes but medullary bone involvement does confer a higher risk of positive bone margins. MM and appropriate adjuvant treatment is an effective strategy for treatment of OCSCC in selected patients with primary tumors adherent to or in proximity to the mandible.