BackgroundIt is elusive which subtypes of immune cells are pivotal in cancer progression and prognosis in gastric cancer (GC). The aim of this study is to clarify clinical impact of immature myeloid-derived immune cells in patients with GC who underwent curative gastrectomy with curative lymphadenectomy and treated with S-1 (tegafur/gimeracil/oteracil) postoperatively. MethodsThe prognostic impact of recruited CD33+ immature myeloid-derived cells were clinicopathologically analyzed in curatively resected stage II and III GC. Correlation of preoperative peripheral leukocyte fractions with recruited CD33+ immature cells was also assessed. ResultsPatients with high CD33+ cell counts in primary tumor showed dramatically worse prognosis (5-y recurrence-free survival 29.0%) than that of the counterparts (79.4%). High CD33+ cell counts independently predicted poor prognosis in stage II/III (hazard ratio, 4.34; P < 0.001). In analyses of each stage, high CD33+ cell count was pivotally associated with poor prognosis in both stages. There was no significant correlation of each peripheral leukocyte fraction with CD33+ cell recruitment. Of note, high CD33+ cell count was significantly correlated with hematogenous recurrence. ConclusionsRecruitment of CD33+ immature myeloid cells critically predict hematogenous recurrences in curatively resected advanced GC. These results give rational to focusing on CD33+ myeloid-derived cells as a novel approach to tackle advanced GC.