Staging Significance of Bone Invasion in Oral Squamous Cell Carcinoma

Objectives: The 2010 American Joint Committee on Cancer recommended that oral squamous cell carcinoma(SCC) that invades adjacent structures through a cortical bone be classified as T4a. It is reported that tumor size T1 to T3 should be elevated by one T-stage in case of bone marrow invasion. A study was undertaken to confirm the precise relationship between bone invasion and disease progression.
Methods: This study is a retrospective review of 325 patients with oral SCC undergoing surgery. Kaplan-Meier analysis was performed to assess the effects of bone marrow invasion on 5-year disease progression-free survival(PFS). In T2 tumors, bone invasion was defined as one or two cortical bone destructions and tested for association with disease progression. Cox’s model was used to assess the effects of bone invasion on PFS after controlling for the potential confounding effects of regional lymph nodal status, surgical margin involvement, perineural invasion, vascular invasion, and adjuvant treatment.
Results: Within the subset of patients with medullary invasion, survival rate varied according to tumor size. Only T3 cases showed significant association with the PFS(p=0.044). In T2 tumors, invasion through two cortical bones was a significant risk factor for disease progression with an adjusted hazard ratio for one cortical bone destruction(p=0.006) or no invasion(HR,2.422; p=0.039). After adjusting for potential confounding factors in multivariate analysis, there was significant association between T status elevated by one T-stage in the event of bony destruction and the PFS(p=0.008, T2 HR,0.993; p=0.985, T3 HR,1.086; p=0.825, T4 HR,2.530; p=0.010). According to the results of multivariate analysis, nodal status(N1 HR,2.308; p=0.008, N2 HR,2.182; p=0.008) and perineural invasion(HR,3.115; p=0.000) were associated with adverse outcomes.
Conclusions: The recommendation that tumors be classified as T1 to T3 based on size and then upstaged by one T-stage in the presence of medullary bone invasion can be accepted. In addition, this study suggests that T2 tumors invading through two cortical bones should be classified as T4.