Abstract
Outcome of adult acute lymphoblastic leukemia (ALL) continues to be poor, and parameters to better discriminate patients with distinct prognosis are necessary. In studies comparing global gene expression differences between normal hematopoietic cells (whole bone marrow, peripheral blood, CD34+, and CD22+ sorted populations) and ALL cells using microarrays we found that the B-ALL cells showed evidence of increased expression of Connective Tissue Growth Factor (CTGF). The median log 2 transformed signal intensity of CTGF was 4.26 (range 3.95–4.76) in normal hematopoietic cells, and 6.59 (range: 3.85–10.62) in all leukemic samples; this difference in signal intensity is equivalent to a 5-fold increase in median expression of CTGF in leukemic cells. Therefore, we hypothesized that expression level of CTGF may have prognostic significance in adult ALL. Using real-time RT-PCR assays for CTGF we examined the expression of CTGF in 79 diagnostic ALL patients from SWOG protocol S9400 (28 bone marrow and 51 peripheral blood samples). Patients with L3 ALL were excluded from the study. The median age of patients was 35 (range 17–64), with the median WBC 23,400/ul (range 600–396,600), and peripheral blood blasts 56% (range: 0–98). Fifty patients had B-ALL (63%), 13 (16%) had T-ALL and lineage was unknown for 16 (20%). When treated as a continuous variable in a logistic regression model, the level of CTGF expression was significantly associated with inferior OS and DFS (p=0.007 and p=0.0012, respectively). When controlled for WBC and cell lineage, the association of CTGF with OS and DFS remained statistically significant. We then sub-grouped the ALL patients into three equal groups (tertiales) based on CTGF expression. This subgroup analysis found that the OS for patients in the highest tertile (highest CTGF expression) was approximately 11% (95% CI 0–24) at 5 years, as compared to 42% (95% CI 23–61) and 58% (95% CI 38–78) for patients with middle and low CTGF expression respectively (figure). In sub-analysis of patients with B-lineage ALL (n=50), the association of CTGF expression with OS and DFS was still statistically significant (p=0.009 and p=0.005) when treated as a continuous variable. This report is an example where a gene expression study detected a gene differentially expressed in leukemia, with clear clinical value. Moreover, this is the first report that correlates the level of expression of CTGF with outcome in ALL patients. We are actively pursuing the biological and clinical significance of CTGF in other ALL patients and model systems.
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