AbstractThe recently developed Cytodiff flow cytometric system (Beckman Coulter, Miami, FL) enables leukocyte analysis using a single immunophenotyping panel tube composed of six markers and five colors and that can detect 16 leukocyte subpopulations. We performed a preliminary investigation of whether changes in any of 16 leukocyte differentials were associated with survival and treatment outcomes in patients with metastatic carcinoma or not.We measured 16 leukocyte differential counts using the Cytodiff flow cytometric system in peripheral blood samples from 40 patients with metastatic malignancy (27 stomach cancer and 13 lung cancer) before chemotherapy and at 15 day intervals after chemotherapy for 2 months.A higher percentage of CD16+ cytotoxic NK+T lymphocytes was found to be the only significant prognostic factor among by Cox regression analysis and a higher percentage of CD16+ cytotoxic NK+T lymphocytes (>5.0%) showed significantly longer survival outcomes by Kaplan–Meier analysis (P = 0.003).The Cytodiff system enables 16 leukocyte subpopulations in a one tube assay and also can operate with only small amounts of sample, although it cannot differentiate NK cells from T lymphocytes. Hence, the monitoring of all leukocyte subpopulations using Cytodiff flow cytometry may be a helpful prognostic tool for patients with metastatic carcinoma. © 2012 International Clinical Cytometry Society