[1054] Phenotypic Characterization of Primary Testicular Diffuse Large B-Cell Lymphoma

Philip Th Went, Thomas Menter, Martina Ernst, Stephan Dirnhofer, Andre Barghorn, Alexandar Tzankov. Institute of Pathology, Basel, Switzerland; Institute of Pathology, Liestal, Switzerland; Medica, Zürich, Switzerland

Background: Primary testicular lymphoma is rare, consisting of 3-5% of primary extranodal lymphomas. Different lymphoma types can occur; however, diffuse large B-cell lymphoma (tDLBCL) represents by far the most frequent subtype. Patients with tDLBCL may not benefit equally from Rituximab therapy as patients with nodal DLBCL. According to recent studies, the incidence of tDLBCL is increasing. To investigate if this is paralleled by a shift in histological morphology, we systematically analyzed the morphology and phenotype of tDLBCL on the background of recently described subtypes.
Design: Forty-three patients from three different Swiss hospitals were included in this study. The tumors were diagnosed between 1972 and 2009. The protein expression profile was assessed by immunohistochemistry.
Results: 39 of the tumors showed centroblastic and one immunoblastic morphology, three were not classifiable. All cases (n=43) were positive for CD79a. According to the Tally algorithm, 83% (n=36) were phenotypically classified as non-GC type. All tumors were EBER negative. 70% (n=30) of the tumors showed active STAT signaling by expression of either pSTAT1 or pSTAT3, but not pSTAT5. P53 staining was positive in five tumors, but p21 staining was negative in all cases, indicating the absence of TP53 mutation. Mean mitotic index was 18/mm2, median MIB1 labeling index was 40% (+/-25%). Tumors with lymphoepithelial lesions in seminiferious tubules showed a higher mitotic activity, although the association was weak. Interestingly, one tumor was positive for Oct4. All 43 cases were negative for NUT1 and PLAP. Only limited clinical data were available: mean age at diagnosis was 69 years (range: 43-87 years, n=41). There was no side predilection of the tumors. One tumor was bilateral at diagnosis, one tumor presented simultaneously in the testis and the CNS. Of ten tumors, five did not relapse (mean follow up time 48 months, min 0, max 132). Five tDLBCL relapsed, thereof two in the contralateral testis, two in the CNS and one in the skin.
Conclusions: We conclude that in tDLBCL centroblastic morphology and a non-GC phenotype predominates. There was no change of morphology or protein expression profile over time. No sign of TP53 mutations was detected. STAT signaling pathway is active and mediated through STAT3 and STAT3. To avoid misdiagnosis, a marker panel should be utilized, as rare cases can be positive for the germ cell tumor marker Oct4.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 139, Monday Afternoon

 

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