Proposed Modification Incorporating Depth of Invasion in Primary Staging for Oral Cancer
In an analysis reported in JAMA Otolaryngology-Head & Neck Surgery, the International Consortium for Outcome Research (ICOR) in Head and Neck Cancer proposed modifying the current American Joint Committee on Cancer (AJCC) staging system for oral cancer to include depth of invasion. A model incorporating depth of invasion was shown to improve prognostic performance of T staging compared with current AJCC staging.
Study Details
The study involved a retrospective analysis of data from 3,149 patients with oral squamous cell carcinoma treated with curative intent with surgery with or without adjuvant therapy at 11 comprehensive cancer centers worldwide between 1990 and 2011. Median follow-up was 40 months.
Mean and median depths of invasion were 12.9 mm and 10.0 mm, respectively. Increasing depth of invasion was significantly associated with more advanced disease, including higher pT category (P < .001) and pN category (P < .001), extracapsular spread (P < .001), and involved margins (P < .001). Multivariate analysis adjusting for pT category, pN category, adjuvant therapy, and time of treatment showed that depth of invasion was significantly associated with disease-specific survival (hazard ratio [HR] = 1.31, P < .001). No between-institutional heterogeneity in prognostic effect was observed (I2 = 6.3%, P = .38).
Modified Staging
Based on Akaike information criterion (AIC), optimal depth of invasion cutpoints were identified as < 5 mm vs ≥ 5 mm in pT category I disease and > 10 mm vs ≥ 10 mm in pT categories II, III, and IV disease. A modified T staging model incorporating these cutpoints was constructed: T1 = AJCC T1, maximum depth of invasion < 5 mm; T2 = AJCC T1, maximum ≥ 5 mm, or AJCC T2, maximum < 10 mm; T3 = AJCC T2, maximum ≥ 10 mm, or AJCC T3-4, maximum < 10 mm; and T4 = AJCC T3-4, maximum ≥ 10 mm. This model outperformed AJCC staging on the basis of lower AIC (P < .001), visual inspection of Kaplan-Meier curves, and significant improvement in bootstrapped C-index (P = .007). Five-year disease-specific mortality for the model vs AJCC staging was 4% vs 8% for T1, 13% vs 18% for T2, 24% vs 35% for T3, and 37% vs 34% for T4 disease.
Compared with AJCC staging, use of the modified model resulted in unchanged T category in 58.1% of patients, upstaging in 32.5%, and downstaging in 9.4%. According to stage, 62.8% of patients with T1 disease were upstaged to T2 based on depth of invasion ≥ 5 mm, 46.8% of patients with T2 disease were upstaged to T3 based on depth of invasion ≥ 10 mm, 71.9% of patients with T3 disease were upstaged to T4 based on depth of invasion ≥ 10 mm, and 22.4% of patients with T4 disease were downstaged based on depth of invasion <10 mm.
The investigators concluded: “We propose an improved oral cancer T staging system based on incorporation of [depth of invasion] that should be considered in future versions of the AJCC staging system after external validation.”
Ardalan Ebrahimi, MBBS, MPH, of Royal Prince Alfred Hospital, New South Wales, Australia, is the corresponding author for the JAMA Otolaryngology-Head & Neck Surgery article.
The authors reported no conflicts of interest.
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