Background/Objectives: Mechanisms underlying treatment resistance in hematopoietic malignancies such as acute lymphoblastic leukemia (ALL) include (1) enhanced activity of anticancer drug efflux mechanisms (MRP1); (2) suppressed activity of anticancer drug influx mechanisms (ENT-1); (3) enhanced drug detoxification activity (AKR1B10, AKR1C3, CYP3A4); (4) influence of the tumor microenvironment (GRP94), etc. We conducted this study to comprehensively and clinically examine treatment resistance due primarily to a decrease in the tumor intracellular anticancer drug concentrations. Methods: The subjects were 19 ALL patients who underwent initial induction therapy with alternating Hyper CVAD/MA therapy. Antibodies against 23 types of treatment resistance-associated proteins were used for immunohistochemical analysis of tumor specimens obtained from the patients, and correlations between the results of immunohistochemistry and the overall survival (OS) were retrospectively analyzed using the Kaplan–Meier method. Results: Based on the patterns of expression of the enzymes involved in treatment resistance, we classified the patients (Urayasu classification for ALL, which we believe would be very useful for accurately stratifying patients with ALL according to the predicted prognosis), as follows: Good prognosis group, n = 1, 5%: AKR1B1(+)/AKR1B10(−), 5-year overall survival (OS), 100%; Intermediate prognosis-1 group, n = 9, 5%: AKR1B1(−)/AKR1B10(−) plus MRP1(−), 5-year OS, 68%; Intermediate-2 prognosis group, n = 6.3%: AKR1B1(−)/AKR1B10(−) plus MRP1(+), median survival, 17 months, 5-year OS, 20%; and Poor prognosis group, n = 3, 16%: AKR1B1(−)/AKR1B10(+), median survival, 18 months, 5-year OS, 0%. n = 2. Conclusions: The Urayasu classification for ALL is considered reliable for predicting the prognosis of patients with ALL after the initial Hyper CVAD/MA remission induction therapy.
Mitsumori et al. (2026) studied this question.