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p0.510.160.11analysis, which is inconsistent with previous studies showing that well-differentiated esophageal cancer is associated with good survival7). This may be attributable to a difference of definitions between Japan and Western countries, since the degree of differentiation is based on the dominant type in Japan, but on the poorest type in Western coun-tries. For example, when the well-differentiated region is dominant and the moderately differenti-ated part is small in esophageal cancer, the Japa-nese pathological diagnosis is well-differentiated, but the Western diagnosis would be moderately differentiated. Furthermore, our small cohort did not include any poorly differentiated cases, and this may also have affected the results.There are several methods for diagnosis of micrometastases: immunostaining of lymph nodes, as performed in this study; lymph node detection Figure 2　Survival curves based on extent of differentiation. There was a significant difference in survival rate between differentiation grades (p=0.031).Table 4　Multivariate Cox regression analysis for degree of differentiation, Stage and micrometastasisDegree of differentiationStageMicrometastasisWell vs. ModerateIII, IV vs. I, IIPositive vs. NegativeHazard ratio1.52.82.7by reverse transcription-polymerase chain reac-tion (RT-PCR); and immunostaining or RT-PCR using peripheral blood. One problem with use of resected lymph nodes is that the results are avail-able only after surgery. Adjuvant therapy after esophageal cancer resection is not the standard in Japan, and there is no effective evidence-based adjuvant treatment, even if a poor prognosis is predicted. Recently, however, it has been shown that administration of nivolumab after esophagec-tomy following preoperative chemoradiotherapy leads to an improved prognosis in patients without pathological complete response (pCR)12), and this treatment has been covered by health insurance in Japan from 2021. Micrometastasis-positive patients might be eligible for adjuvant therapy even if their carcinoma is pN0 or pN1.This study has some limitations. First, it was not Confidence intervals0.4 - 5.50.7 - 120.8 - 9.1367