Definition of prognostic subgroups in the T3 stage of the eighth edition of the American Joint Committee on Cancer staging system for cutaneous squamous cell carcinoma: Tentative T3 stage subclassification.

Background: Although the eighth edition of the American Joint Committee on Cancer staging system (AJCC8) provides improved prognosis stratification of cutaneous squamous cell carcinoma (CSCC) over AJCC7, T3 has a variable prognosis.

Objective: To define prognostic subgroups in T3-AJCC8 CSCC.

Methods: Retrospective cohort study of 196 primary T3-AJCC8 CSCCs. We conducted multidimensional scaling analysis using the 6 risk factors that define T3 CSCCs. The prognoses of the groups obtained were analyzed by means of competing risk analysis.

Results: Group 1 was characterized by a tumor thickness greater than 6 mm (without invasion beyond the subcutaneous fat), alone or in combination with a tumor width of at least 4 cm. Group 2 was characterized by the presence of either invasion beyond the subcutaneous fat or by the involvement of nerves (≥0.1 mm, or deeper than the dermis). Group 3 was characterized by the combination of both T3b risk factors, or of 3 or more risk factors. Group 3 (tentatively named T3c) patients had the worst prognosis for disease-specific poor outcome events and major events, Group 2 (T3b) had intermediate risk, and Group 1 (T3a) had the best prognosis (disease-specific poor outcome events: hazard ratio [HR], 1.94; P = .00009; major events: HR, 2.55; P = .00001; disease-specific death: HR, 10.25; P = .0009).

Limitations: Retrospective study.

Conclusions: There is statistically significant evidence that T3-AJCC8 may be classified into distinct prognostic subgroups.