Effects of multidrug resistance gene expression in acute erythroleukemia.

Acute erythroleukemia is a relatively rare disorder of a multilineal nature. Patients with this type of leukemia traditionally have been treated with a standard myeloid protocol, with a wide variation in prognosis between M6a, which has a similar prognosis to acute myelogenous leukemias, and M6b, with an extremely poor outcome despite aggressive therapy. Forty-eight archival cases of acute erythroleukemia, subtypes M6a (the traditional FAB-M6), M6b (pure erythroleukemia), and M6c (>30% myeloblasts and >30% pronormoblasts by FAB exclusion criteria), were evaluated for multidrug resistance gene (MDR-1) status. Findings were correlated with clinical course and karyotypes. Immunohistochemical stain for the protein product of MDR-1, P-glycoprotein, was variably positive in 11 of 23 patients with M6a, as well as in all of the patients with M6b (strongly positive) and M6c (weakly positive). P-glycoprotein expression positively correlated with unfavorable cytogenetic aberrations, poor response to chemotherapeutic agents, and short survival. Most significant was that P-glycoprotein expression demonstrated a negative additive effect on response to treatment and prognosis with unfavorable cytogenetic anomalies. P-glycoprotein expression and multiple cytogenetic anomalies most probably contribute to the resistance to chemotherapy and poor survival characteristic of the patients with M6b (mean survival, 3.15 +/- 4.2 mo) and M6c (mean survival, 10.5 +/- 12.7 mo). Because patients with M6b and M6c have increased numbers of pronormoblasts in their bone marrow and past chemotherapeutic attempts have failed, chemotherapy directed at these cells is appropriate. Additional therapy directed toward the MDR-1 gene and its protein product seems indicated from our findings.