Abstract
Primary extranodal malignant lymphoma of the thyroid is a rare entity composed of mostly neoplastic transformation of germinal center-like B cells (GCB) or memory B cells. Other B-cell-type malignancies arising primarily in the thyroid have rarely been described. Immunohistochemical examination of autopsied primary malignant lymphoma of the thyroid in an 83-year-old Japanese female revealed the presence of a non-GCB subtype of diffuse large B-cell lymphoma (DLBCL) without the typical codon 206 or 265 missense mutation of MYD88. The lack of the highly oncogenic MYD88 gene mutation, frequently observed in DLBCL of the activated B-cell (ABC) subtype, and the detection of an extremely aggressive yet local clinical phenotype demonstrated that the present case was an exceptional entity of the type3 (non-GCB and non-ABC) subtype.