Expression of MYC but Not pSTAT3 Is an Adverse Prognostic Factor for Diffuse Large B Cell Lymphoma (DLBCL) Treated with Epratuzumab/R-CHOP

Abstract 1575

We recently demonstrated in a phase II study that the anti-CD22 monoclonal antibody epratuzumab added to RCHOP improved DLBCL survival parameters. Despite these advances, 30–40% of DLBCL patients still relapse and die of disease. Recent advances have led to the identification of a variety of intracellular oncogenic pathways as potential targets for lymphoma therapy. Specifically, many studies have found that activation of the Signal transducer and activator of transcription 3 (STAT3) pathway promotes tumor cell survival in various types of cancers. STAT3 is a transcription factor and exerts its anti-apoptototic effect through several downstream targets such as MYC. MYC protein can be expressed in lymphoma cells with or without the presence of MYC translocation. The frequency of phosphorylated STAT3 (pSTAT3) and MYC expression and their prognostic relevance are unknown within diffuse large B-cell lymphoma (DLBCL), germinal center B-cell (GCB) and non-GCB subtypes. This study studied the tumor cell expression of pSTAT3 and MYC by IHC paired with serum cytokine levels in a DLBCL patient population uniformly treated on N0489.

DLBCL tumor samples (n=38) were stained for detection of nuclear pSTAT3 expression. Using a threshold of ≥30% of tumor nuclei staining positive, 35 % (14/40) of tumors were pSTAT3+. An additional 17% (7/40) had between 10–30% pSTAT3+ cells. Non-malignant tonsil tissues (n=10) were positive for tSTAT3 in all cases but all but one case were pSTAT3 negative. Twenty-four of the same DLBCL tumors used for pSTAT3 expression were stained for MYC and 50% (12/24) were MYC positive (all nuclear) as defined by the criteria of ≥30% of cells staining positive. In cases (n=23) where both MYC and pSTAT3 IHC were performed, a positive pSTAT3 was more likely to have MYC expression whereas a positive MYC stain did not inform pSTAT3. By using a break apart probe for the MYC gene, MYC translocations in the major breakpoint regions were found in 10% (3/29) of cases. When MYC FISH was correlated with MYC IHC in the 24 DLBCL cases that had both techniques performed, all 3 MYC translocation cases were GCB by IHC, two were strongly positive for MYC by IHC, and 1 was negative. Among the 21 MYC FISH negative cases, 10 were MYC positive by IHC. These data suggest that MYC expression in lymphoma is not only controlled by genetic events such as translocations but also by other signaling pathways such as STAT3. pSTAT3 expression was correlated with an elevated serum LDH (p=0.0007). Neither MYC or pSTAT3 tumor expression correlated with other clinical or pathological features. Survival analysis revealed a trend toward shorter EFS for DLBCL patients whose tumors expressed MYC protein by IHC (p=0.2) or had a MYC translocation (p=0.09) by FISH; pSTAT3 expression status did not predict EFS (p=0.9). Within the GCB group 10 cases were MYC negative (10/17; 59%) and 7 cases were MYC positive (7/17; 41%). Among the non-GCB group 83% (5/6) were MYC positive. These data clearly suggest a trend of higher MYC positivity in the non-GCB DLBCL group (p=0.07). MYC positive cases had a clear trend of inferior EFS in both GCB (p=0.2) and in non-GCB (p=0.5) groups. The distribution of pSTAT3 (n=38) expression was also evaluated in the GCB (n=26) and non-GCB (n=12) DLBCL. In the GCB group 27% (7/26) were pSTAT3 positive compared to 58% (7/12) in the non-GCB group. Thus, there was a clear trend toward higher pSTAT3 positivity in non-GCB DLBCL tumors (p=0.06); however, pSTAT3 status did not correlate with EFS in either GCB or non-GCB DLBCL patients. In the present study we correlated pretreatment serum cytokines levels of these patients with pSTAT3 and MYC tumor cell expression. Out of the 30 cytokines tested, the only pre-treatment cytokines that were significantly correlated with pSTAT3 expression were IL-10 (p=0.05), G-CSF (p=0.03) and TNFa (p=0.04); none were correlated with MYC expression.

Overall, our data provide evidence that over-expression of pSTAT3 and MYC is common in DLBCL. These biomarkers have potential as prognostic factors in the case of MYC and as a tool for selecting therapy for pSTAT3. MYC may be especially useful to further identify an adverse group of DLBCL patients within the otherwise favorable GCB tumor group. The availability of JAK/STAT and STAT-specific inhibitors provides the rationale to incorporate pSTAT3 staining in tumors from patients who are participating in these trials to learn if this biomarker can predict response