Immunohistochemical Expression Patterns of Germinal Center and Activation B-Cell Markers in Diffuse Large B-Cell Lymphoma. Clinicopathologic Study of 62 Cases from Peru.

Background: Recent studies have shown that diffuse large B-cell lymphoma (DLBCL) cases with gene expression profiles similar to germinal center (GC) B cells had a much better prognosis than DLBCL cases with gene expression profiles resembling activated B cells. DLBCL can be classified into three immunohistochemical expression patterns: GC B-cell pattern (pattern A) expressing CD10 and/or Bcl-6 but not MUM1; activated GC B-cell pattern (pattern B) expressing at least one of GC B-cell markers and MUM1; and activated non-GC B-cell pattern (pattern C) expressing MUM1 but not GC B-cell markers.

Purpose: To determine the frequency of these patterns, the immunohistochemical expression intensity of MUM1, BCL6 and BCL2, as well as International Prognostic Index (IPI) and therapeutical response.

Methods: Immunohistochemical analysis on paraffin-embedded tissues was performed using the streptavidin-avidin-biotin method in 62 cases of DLBCL. The intensity of immunohistochemical expression was performed as follows: positive (more than 50% expression), positive/negative (expression 20 to 50%), and negative (less than 20%expression).

Results: The average age was 60 years. Females were slightly more frequent than males. 84% cases were primary nodal. According to IPI, 60% of cases were low (L) or intermediate-low (IL) risk, and 40% were intermediate-high (IH) or high risk (H). The corresponding A, B and C patterns, by immunohistochemistry, were 10%, 19% and 65% respectively. The majority of patients were treated with CHOP. Complete response (CR) was achieved in 54%, partial response (PR) in 11%, and no response (NR) in 23%. 9 % were not assessed. 4/6, 8/10, 17/36 of the cases had CR in the patterns A, B, C respectively. 5/6, 8/12, 22/40 of the cases were L-IL in the same patterns, without significant difference between these groups. The immunohistochemical expression intensity for either marker was not statistically significant.

Conclusions: The most frecuent pattern was C. The activated patterns were most common. The correlation between different pattern expression, IPI and therapeutical response didn’t show statistical differences, probably due to the small size of the sample.