Risk Stratification Combining MYC Immunohistochemistry with Standard IPI Has Utility in Patients with Diffuse Large B-Cell Lymphoma

Background

Though the majority of patients (pts) with newly diagnosed diffuse large B-cell lymphoma (DLBCL) are curable with R-CHOP chemotherapy, a significant proportion will relapse or have refractory disease. The most commonly used clinical tool is the international prognostic index (IPI), though this cannot fully capture the heterogeneity of cases seen in practice. In recent years biomarkers such as MYC are entering clinical use. Pts with lymphomas demonstrating dual abnormalities of MYC in association with BCL2 and/or BCL6- known as ‘double-hit’ lymphomas are consistently shown to have poorer disease free and overall survival. While Fluorescence in-situ hybridization (FISH) for MYC translocation is the gold-standard, immunohistochemistry (IHC) is faster and significantly cheaper. Studies in recent years have confirmed the prognostic significance of increased MYC expression by IHC. Due to significant inter-laboratory variability however, internal validation is required.

Methods

Tissue samples of pts treated at Royal North Shore Hospital in Sydney, Australia between 2003-2012 were retrospectively assessed. Pts were included if they were transplant eligible (age <70 years), and had been treated for de novo DLBCL with a rituximab containing regimen. Samples were scored for MYC IHC as well as BCL2 and BCL6. Clinical data including IPI score, treatment and outcomes were also collected. Treatments were stratified into standard R-CHOP-like versus more intensive regimens including R-Hyper-CVAD and dose-adjusted R-EPOCH.

A significant cut-off for MYC staining was determined using X-Tile (Rimmlab, New Haven, CT) and confirmed with the log-rank test. Estimation of OS and EFS was performed using the Kaplan-Meier method. Pt characteristics were compared using Chi-squared test. Statistical analysis was performed using MedCalc 15.4 (MedCalc software, Ostend, Belgium). Ethics approval was received for a retrospective study.

Results

105 patients met study criteria. The 5 year OS and EFS was 86% and 77% respectively (Figure 1 and 2). The optimal cut-off for positive MYC IHC was >70%. This was seen in 23% of samples. From the 13 cases with MYC FISH results, the positive and negative predictive values of positive MYC IHC were 50% and 92% respectively. There was no significant difference between the MYC positive and negative groups with respect to demographics or IPI score (Table 1). Significantly more patients with MYC positivity received intensive treatment (37% versus 16%, p=0.047). Despite this, 5 year OS was significantly poorer at 51% versus 87% at median follow-up of 40 months (P=0.0025, Figure 3). There was a trend towards worse EFS at 61% versus 75% though this did not reach statistical significance (P=0.242). On multivariate analysis, MYC IHC and IPI score were the only independent prognostic factors. Based on the relative odds ratio, a combined scoring system was designed, attributing 1 point for positive MYC IHC and/ or IPI intermediate-high risk, and 2 points for IPI high risk. This resulted in 4 risk groups with significantly different 5 year OS of 94%, 78%, 45% and 0% (P<0.0001).

Discussion

MYC IHC is of independent prognostic significance. Due to significant variability between laboratories, local validation is required. A composite score combining IPI and MYC IHC is simple to calculate and may provide better prognostic utility than either factor alone. Ongoing prospective studies investigating the role of clinical risk stratification and newer biomarkers are required to identify patients likely to need more intensive or novel therapies.