Nomogram for Risk-Adaptive Estimation of the Locoregional Control Benefit Following Postoperative Radiation Therapy for Pathologic N0 Oral Cavity Cancer: A Retrospective Analysis

Purpose We constructed a nomogram to define the risk of locoregional failure (LRF) and quantify the association between postoperative radiation therapy (PORT) and LRF, for patients with pathologic T (pT)1 to pT4 N0 oral cavity squamous cell carcinoma (OSCC). Methods and Materials pT1 to PT4N0M0 OSCC cases treated between 1994 and 2017 at 4 tertiary cancer centers were reviewed. Prognostic factors (P < .05) identified in multivariable analysis and clinicopathologically relevant characteristics were used to construct a nomogram to define LRF risk group classification. Subsequently, the association of PORT with outcomes was calculated for each individual risk group. Results A total of 1094 patients were retrospectively reviewed. Median follow-up was 4.7 years (IQR, 2.9-6.4 years). The nomogram comprised 6 statistically significant factors (pT category, histologic grade, perineural invasion, compromised resection margin [close <5 mm, positive or undetermined], inadequate neck dissection [<18 lymph nodes resected at any side of the planned neck dissection], and nonutilization of PORT), and 3 clinicopathologically relevant factors (oral tongue subsite, lymphovascular invasion, and smoking history). Risk scores were generated by summing the points of the coefficients in the above model, excluding the coefficient of PORT. Four risk groups were identified based on the 3-year LRF probability: low, standard, intermediate, and high (3-year LRF: 6%, 12%, 23%, and 27%, respectively, P < .001). The model demonstrated a C-index of 0.66, indicating that approximately 1 in 3 patients may be misclassified. The use of PORT was associated with a significant reduction of the 3-year LRF in the intermediate- and high-risk groups (19% vs 28%, P = .02 and 22% vs 38%, P = .03, respectively), which translated into improved 3-year overall survival rates (78% vs 70%, P = .04 and 73% vs 45%, P < .001, in the intermediate- and high-risk groups, respectively). Conclusions Our nomogram and risk group classification could be a clinically relevant tool to facilitate treatment-decision making in the adjuvant setting for individual pT1 to pT4N0M0 OSCC patients based on an estimation of PORT benefit for LRF. The results from this retrospective study must be interpreted with caution, and our proposed model requires validation using prospective data before it can be applied in practice.