Oral Squamous Cell Carcinoma: Histologic Risk Assessment, but Not Margin Status, Is Strongly Predictive of Local Disease-free and Overall Survival

Abstract

To analyze the impact of resection margin status and histologic prognosticators on local recurrence (LR) and overall survival (OS) for patients with oral squamous cell carcinoma (OSCC). This study was both retrospective and prospective in design. Cohort 1 refers to the entire group of 292 patients with OSCC. The slides from the earliest resection specimens from Cohort 1 were examined in an exploratory manner for multiple parameters. Cohort 2 refers to a subset of 203 patients, who did not receive any neoadjuvant therapy and had outcome data. Cohort 3 represents a subset of Cohort 2 (n = 168) wherein the histologic resection margin status could be reconfirmed. Cohort 4 refers a subset of 85 patients with tongue/floor of mouth tumors. Margin status was designated as follows: group 1, clearance of > or =5 mm with intraoperative analysis, no need for supplemental margins (n = 46); group 2, initial margins were measured as <5 mm during intraoperative frozen section; supplemental resection margins were negative on final pathology (n = 73); group 3, the final pathology revealed resection margins <5 mm (n = 30); group 4, the final pathology revealed frankly positive resection margins (n = 19). The endpoints of LR and OS were queried with respect to T stage, tumor site, margin status, and numerous histologic variables, by Cox regression and Kaplan-Meier survival analyses. Tumor stage (T) was significantly associated with LR (P = 0.028). Kaplan-Meier analysis for stage and for intraoral site was significantly associated with LR for T4 tumors. The increased likelihood of LR was higher for T4 OSCC of the buccal mucosa (75%), sinopalate (50%), and gingiva (100%) compared with mobile tongue (27%), and oropharynx (13%) (P = 0.013). Margin status was not associated with LR or OS (Cohort 3). This was so when all tumors were grouped together and when separate analyses were performed by tumor stage and oral subsite. No significance was demonstrated when margin status was examined for patients with similar treatment (surgery alone or surgery with adjuvant RT). However, the administration of adjuvant RT did significantly increase local disease-free survival (P = 0.0027 and P = 0.001 for T1 and T2 SCC, respectively). On exploratory analyses of histologic parameters, worst pattern of invasion was significantly associated with LR (P = 0.015) and OS (P < 0.001). Perineural invasion involving large nerves (>1 mm) was associated with LR (P = 0.005) and OS (P = 0.039). Limited lymphocytic response was also significantly associated with LR (P = 0.005) and OS (P = 0.001). When used as covariates in a multivariate Cox regression model, worst pattern of invasion, perineural invasion, and lymphocytic response were significant and independent predictors of both LR and OS, even when adjusting for margin status. Thus, these factors were used to generate our risk assessment. Our risk assessment classified patients into low-, intermediate-, or high-risk groups, with respect to LR (P = 0.0004) and OS (P < 0.0001). This classification retained significance when examining patients with uniform treatment. In separate analyses for each risk group, we found that administration of adjuvant radiation therapy is associated with increased local disease-free survival for high-risk patients only (P = 0.0296) but not low-risk or intermediate-risk patients. Resection margin status alone is not an independent predictor of LR and cannot be the sole variable in the decision-making process regarding adjuvant radiation therapy. We suggest that the recommendation for adjuvant radiation therapy be based on, not only traditional factors (inadequate margin, perineural invasion, bone invasion) but also histologic risk assessment. If clinicians want to avoid the debilitation of adjuvant radiation therapy, then a 5-mm margin standard may not be effective in the presence of high-risk score.