Examination of current staging systems in cutaneous squamous cell carcinoma

Introduction: Cutaneous squamous cell carcinoma (cSCC) is the second most prevalent skin cancer with an estimated incidence of 700,000 cases in the United States. Our research examines the AJCC 7th, AJCC 8th and BWH staging systems. Methods: 949 retrospective cases of cSCC were randomly sampled between 2009 to 2016 from the Mayo Clinic Enterprise and stratified to mirror the US population. Chart review was performed to collect patient demographics, tumor characteristics, and outcomes. Results: The mean age was 74.5 (SD 11.8), 65.2% were male, 34.8% were female, and 95.0% were Caucasians. 14.7% of cases were immunosuppressed. 95.8% of tumors were sun exposed. The mean clinical tumor dimension was 1.3 cm (SD 1.0). 78.7% of cases were well-differentiated, 16.5% moderately differentiated, and 4.8% poorly differentiated. AJCC 7th/8th staging was 89.4%/89.5% T1, 9.9%/6.2% T2, 0.3%/3.8% T3, and 0.4%/0.5% T4/T4a+T4b, respectively. BWH staging was 85.7% T1, 10.5% T2a, 2.8% T2b, and 0.9% T3. Poor outcomes occurred with: local recurrence (3.6%), nodal metastasis (2.4%), in-transit metastasis (0.6%) and distant metastasis (0.5%). Metastatic or recurrent disease occurred in BWH, AJCC 7th and AJCC 8th staging, respectively: T1: 2.5%, 2.7% and 2.7%; T2a/T2/T2: 11.0%/27.7%/15.3%; T2b/T3/T3: 63.0%/33.3%/50.0%; T3/T4/T4a,T4b: 55.6%/75.0%/50.0%, 100%. Median disease-free survival (DFS) in months: BWH T1/T2a/T2b/T3: 96.1/39.2/14.5/13.1 (p<0.0001) with T2a/T2b/T3 hazard ratios (HR) of 2.62/5.13/8.59 (p<0.0001); AJCC 7th T1/T2/T3/T4: 95.1/32.5/NE/6.7 (p <0.0001) with T2/T3/T4 HR of 3.15/2.90/15.62 (p <0.0001/0.29/<0.0001); AJCC 8th T1/T2/T3/T4a/T4b: 95.1/33.1/10.9/NE/13.1 (p <0.0001) with T2/T3/T4a/T4b HR of 2.37/5.81/10.23/12.23 (p <0.0001/<0.0001/0.001/0.01). Conclusion: Current staging systems predict poor outcomes and DFS. However, BWH staging may offer better stratification in predicting poor outcomes whereas AJCC 8th may offer better DFS risk stratification in intermediate to high risk cSCC.