CD5-positive follicular lymphoma characterized by CD25, MUM1, low frequency of t(14;18) and poor prognosis.

CD5-positive follicular lymphoma (FL), although rare, has been described in a number of case reports. However, a statistically valid, clinicopathological comparison between CD5-positive FL and CD5-negative FL has never been performed because of its rarity. We statistically compared clinicopathological characteristics of 22 cases of CD5-positive FL, diagnosed by immunohistochemistry, flow cytometry and morphological findings, with those of 62 cases of FL without CD5 expression (control cases). CD5-positive FL patients showed a higher tendency of peripheral blood involvement (P = 0.076) and a higher frequency of CD25 expression (P = 0.0004) and MUM1 protein expression (P = 0.0008), and a lower frequency of t(14;18)(q32;q21) (P = 0.017). The overall survival (OS) curve of CD5-positive FL was significantly worse than that of control cases (P = 0.0266), although progression-free survival curves did not show a significant difference (P = 0.7899). Moreover, CD5 expression was shown to be an independent poor prognostic factor for OS in both univariate analysis [Hazard Ratio (HR), 3.63; P = 0.0464] and multivariate analysis (HR, 57.16; P = 0.0001). CD5-positive FL showed different clinicopathological characteristics from FL lacking CD5 expression. These results suggest that CD5-positive FL should be considered a different type of FL, and its clinicopathological management should be conducted differently.