►This case is an unusual presentation of a rare disease entity. ►The diagnosis of epithelioid trophoblastic tumor can be challenging resulting in delay in diagnosis. ►Epithelioid trophoblastic tumor can have a very aggressive course, especially in metastatic disease.

CD10, BCL-6, and MUM1 are commonly used immunohistochemical (IHC) stains for classifying diffuse large Bcell lymphoma (DLBCL), and considered to predict outcome. Our objective is to correlate expression of CD23, CD10, BCL-2, BCL-6, MUM1, and Ki-67 proliferation index response to therapy. A natural language search was performed in our information system using the terms "diffuse large" and "lymphoma" from 2008-2012 (for adequate follow-up). These cases were then reviewed, along with the IHC slides previously performed and interpreted as positive (> 30% expression) or negative. A different reviewer searched individual patients' electronic medical records for treatment response. Treatment response was stratified into 1) complete response (CR) to one modality, 2) moderate response (MR) with achievement of remission by multiple treatment modalities, and 3) no response (NR) to any treatment modalities or death due to DLBCL. Sixty-three cases were reviewed that had sufficient follow-up and clinical information. Pearson χ 2 and Fisher exact tests were employed to detect statistical significance (2-sided P < .05) of IHC expression with treatment response as well as expression of the markers of interest with each other. Of those tumors with high ki67 expression (defined as > 80%), 8 showed NR (80%), while of those tumors with low ki67 expression (<8 0%), 16 (40%) showed NR (P = .067). Conversely, 25 patients showed CR or MR (61% of low Ki67 tumors). MUM1 expression approached significance, with 80% of negative tumors demonstrating CR, while 70% of positive tumors demonstrated NR (P = .16). CD10, CD23, BCL-2 and BCL-6 expression did not show any association to treatment outcome, and CD23 expression showed a significant association with female gender (P = .004). Ki67 expression remains the best predictor for treatment response/outcome. MUM1 expression also correlates with treatment response and does not seem to be associated with CD10 or BCL-6 expression. CD10 and BCL-6 expression did not predict better or worse treatment response/outcome.