Background: Both cytogenetic and molecular abnormalities have been identified in acute myeloid leukemia (AML) that provide the framework for diagnostic classification and risk-stratification schemes. However, there are currently only a small number of informative prognostic markers, and it is a recurrent clinical observation that this limited battery fails to accurately predict outcome for many patients. This highlights the need for additional and refined tools to characterize disease risk in AML.
Patients and Methods: For gene discovery, gene expression array data from 211 pediatric patients with AML were queried. Subsequently, expression of the gene of interest was quantified in cryopreserved pretreatment specimens from patients enrolled on the AAML03P1 and AAML0531 trials: AAML03P1 was a pilot phase 3 study investigating the feasibility of combining gemtuzumab ozogamicin (GO) with intensive chemotherapy in pediatric patients up to age 30, whereas AAML0531 was a phase 3 study on >1,000 patients testing the value of GO addition to chemotherapy in a randomized fashion. Taqman-based quantitative reverse-transcriptase PCR was used to quantify mRNA expression of the gene of interested and the housekeeping gene, b-glucuronidase (GUSB). Cytogenetics and molecular prognostic markers were used for risk classification as follows: low risk (mutation in core-binding factor, NPM1, or CEBPa), high risk (-5/5q-, monosomy 7, or FLT3-ITD with high allelic ratio), or standard risk (all other patients with cytogenetic/molecular data).
Results: Multimerin-1 (MMRN1), a member of the elastin microfibrillar interface protein (EMILIN)/multimerin family that may mediate cellular adhesion via integrin receptors, was identified in gene expression array data as a gene whose expression varied widely, with expression levels possibly related to patient outcomes. To study this possible relationship further, we quantified MMRN1 mRNA in 183 participants of AAML03P1 and correlated expression levels with clinical outcome. MMRN1 expression varied >80,000-fold relative to GUSB. Patients with the highest MMRN1 expression (4th quartile, corresponding to a relative MMRN1 expression of >0.5) indeed had inferior event-free survival (EFS; P<0.002) and higher relapse risk (P<0.004), suggesting that high MMRN1 expression could serve as adverse prognostic factor in pediatric AML. To further validate these findings, we quantified MMRN1 expression in 750 participants of AAML0531, and correlated expression levels with clinical outcome and disease characteristics. In 740 of the 750 patient specimens, MMRN1 was detectable, varying >130,000-fold relative to GUSB. Using a cut-off for high MMRN1 expression as defined in the AAML03P1 cohort (i.e. relative MMRN1 <0.5 [n=590] vs ≥0.5 [n=160]), we found that patients with high MMRN1 expression had a lower response rate after the first course of induction therapy (67% vs. 77%, p=0.013) and more likely minimal residual disease after this initial chemotherapy cycle (43% vs. 26%, p=0.001). They also had inferior 5-year overall survival (OS; 44±9% vs. 69±4%, p<0.0001), lower 5-year EFS (32±8% vs. 54±4%, p<0.0001), and higher 5-year relapse risk (57±10% vs. 35±5%, p<0.0001). At least partially, these differences could be attributed to associations between MMRN1 expression and disease characteristics. Specifically, patients with high MMRN1 expression were less likely to have low-risk disease (P<0.001), and more likely had standard-risk (P<0.001) or high-risk (P<0.001) disease compared to those with low MMRN1 expression. However, after adjustment for disease risk, age, and treatment arm, high MMRN1 expression remained statistically significantly associated with inferior OS (hazard ratio [HR]=1.37 [95% confidence interval: 1.05-1.86] p=0.022), and a trend toward lower EFS (HR=1.25 [0.98-1.59] p=0.077) in multivariate cox models.
Conclusion: This study identifies high MMRN1 expression as a novel adverse prognostic factor in pediatric AML. Although the association between adverse outcome and high MMRN1 expression is at least partly due to the higher proportion of adverse-risk features among AML patients with high MMRN1 expression, high MMRN1 expression continued to be associated with inferior survival even after adjustment of disease risk.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.