Background: Patients with adventitia-invading (T3) tumors, which account for the majority of esophageal cancers, are indicated for surgery but still have a poor prognosis. Subclassifying T3 tumors based on clinical outcome would be useful for selecting adequate adjuvant therapies. Methods: Using 268 esophageal cancer specimens from patients without preoperative treatment, the length of the vertical and longitudinal tumor invasion, entire esophageal wall thickness, and interruption of the outer muscle layer were measured. These morphological parameters correlated with clinico-pathological factors and outcome. Results: Patients were classified as T1 (38.4 %), T2 (11.9 %), T3 (38.4 %), and T4 (11.2 %) and T stage correlated well with the four morphological parameters (p < 0.0001). Each of the four morphological parameters was a significant prognostic factor. A cutoff at 20 mm of muscle layer interruption (MLI) yielded the highest prognostic significance (5-year survival 36.7 vs. 59.1 %, p = 0.009). T3 tumors with <20 mm MLI showed survival rates equivalent to T2 tumors (5-year survival 59.5 %), whereas those with ≥20 mm MLI had survival rates similar to T4 tumors (5-year survival 26.7 %). Although lymphatic and hematogenic recurrence was not significantly different, local recurrences occurred more frequently in patients with T3 tumors with ≥20 mm MLI than in those with <20 mm MLI (4.3 vs. 21.4 %, p = 0.019). Conclusions: T3 esophageal cancer can be classified into subgroups according to the length of MLI. Additional local treatment would be indicated for T3 tumors with >20 mm MLI.
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