Background: The mitogen‐activated protein kinase (MAPK)/ERK signaling cascade and the phosphoinosytol‐3 phosphate/Akt (PI3K/Akt) pathways are involved in proliferation and differentiation of hematopoietic cells. The frequency of PI3K/Akt and MAPK pathway activation in adult acute lymphoblastic leukemia (ALL) still need to be elucidated.Aims: To assess the activity and prognostic implications of MAPK/ERK and PI3K/Akt pathways in adult (ALL).Methods: We examined 28 precursor‐B‐cell ALL and 6 T‐cell primary ALL samples. Flow cytometry was employed to analyze the expression levels of phosphorylated ERK and phosphorylated Akt.Results: Ten out of 15 (67%) ALL fresh samples (7 B‐cell, 3 T‐cell) showed constitutive p‐ERK expression. The p‐ERK mean fluorescent index ratio (MFI (R)) showed a tendency to be higher in ALL than in normal T lymphocytes (1.26 [0.74–3.10] vs. 1.08 [1.02–1.21], respectively [p = .069]) and was significantly lower than in leukemic cell lines (median MFI (R) 3.83 [3.71–5.97] [p < .001]). Expression of p‐Akt was found in 35% (12/34) (10 B‐cell, 2 T‐cell). The median MFI (R) expression for p‐Akt in primary blast cell was 1.13 (0.48–9.90) compared to 1.01 (1.00–1.20) in normal T lymphocytes (p = ns) and lower than in leukemic cell lines (median MFI (R) 2.10 [1.77–3.40] [p = .037]). Moreover, expression of p‐ERK was negatively associated with the expression of CD34 (1.22 [0.74–1.33] vs. 1.52 [1.15–3.10] for CD34(+) and CD34(−) group, respectively, p = .009).Conclusion: Our findings suggest that both MAPK/ERK and PI3K/Akt are constitutively activated in adult ALL, indicating a targeted therapy potential for ALL by using inhibitors of these pathways.

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