Primary breast diffuse large B-cell lymphoma shows a non-germinal center B-cell phenotype

Primary breast diffuse large B- cell lymphoma has a poor prognosis relative to other extranodal diffuse large B-cell lymphoma. Recently, diffuse large B- cell lymphoma has been subclassified as germinal center B- cell- like and nongerminal center B- cell types using tissue microarrays. The 5- year overall survival rate of the germinal center B- cell group is better than that of the nongerminal center B- cell group. To elucidate the reason for which primary breast diffuse large B- cell lymphoma has a poor clinical outcome, we investigated 15 patients with primary breast diffuse large B- cell lymphoma ( stage IE; 13 cases, stage IIE; two cases) by immunohistochemistry using various markers including CD10, Bcl- 6, MUM1 and MIB- 1 and by molecular analysis of the immunoglobulin heavy chain gene variable region. Immunohistochemistry showed 0/ 15 ( positive cases/ examined cases) for CD10, 5/ 15 for Bcl- 6, 15/ 15 for MUM1, 10/ 15 for Bcl- 2, 2/ 15 for CD5 and 4/ 15 for CD40. The expression pattern of CD10( -) MUM1( +) in primary breast diffuse large B- cell lymphoma corresponded to the nongerminal center B- cell group. Moreover, the MIB- 1 index was distributed from 60 to 95% with a mean of 79%, indicating a high proliferation of the lymphoma cells. The immunoglobulin heavy chain gene variable region of primary breast diffuse large B- cell lymphoma had a mutation frequency of 1 - 10% ( seven cases) and 0 - 1 additional mutations in ongoing mutation analysis ( five cases). Primary breast diffuse large B- cell lymphoma had characteristics of the nongerminal center B- cell group. In conclusion, primary breast diffuse large B- cell lymphoma has a nongerminal center B- cell phenotype and has a high MIB- 1 index. These features might therefore be associated with poor prognosis.