CD20 Antigen May Be Expressed by Reactive or Lymphomatous Cells of Transformed Mycosis Fungoides

Abstract

Mycosis fungoides (MF), the most common primitive cutaneous T-cell lymphoma, can undergo transformation in about 10% of cases. Transformed mycosis fungoides (T-MF) is often associated with the appearance of a CD20 component. The aim of this study was to analyze whether such cells are reactive or lymphomatous and to evaluate their prognostic impact. Among 311 T-MFs from the French Cutaneous Lymphoma Study Group registry, we studied 148 cases. CD20 was expressed in 88 cases (59%). The proportion of CD20 cells among T-MF lesions was <10% for 54 cases (38%), 10% to 49% for 71 cases (81%), and >50% for 17 cases (19%). We focused the study on 23 cases that contained >50% CD20 cells. To evaluate the nature of the CD20 component, we used immunohistochemistry (2 anti-CD20 antibodies, L26 and 7D1 clones, and 2 other anti-B-cell antigen antibodies, CD22 and PAX5) and a double-stain immunofluorescence technique (anti-CD20 and anti-CD3 antibodies). The clonality of B cells was studied by polymerase chain reaction. Three profiles were observed. In 15 of the 23 cases, the CD20 cells were reactive. In 6 cases, CD20 protein was aberrantly expressed in T-MF lesions. Lastly, there were 2 composite lymphomas (T-MF infiltrate with a B-cell follicular lymphoma). In view of this series, we propose a simple algorithm to help pathologists evaluate the nature of the CD20 component associated with T-MF. Although statistically not significant, there was a trend toward a worse prognosis in the presence of >50% CD20 cells and of a nodular perifollicular pattern of this component.

CD8‐positive peripheral T‐cell lymphoma with aberrant expression of CD20 and concurrent in situ follicular lymphoma

“…To our knowledge, 27 T‐cell lymphomas with CD20 expression involving the skin have been published to date. In this location, 19 cases occurred in patients with MF and only 8 were classified as cutaneous PTCL. Notably, the MF cases had clinical and pathological features of aggressiveness, since many patients had disseminated or tumoral disease and many cases had high numbers of large cells.…”

“…Most of those cases had aberrant expression of CD20 and were systemic . Most cases involving the skin were mycosis fungoides (MF) and had cytologic features indicative of aggressive disease . However, although uncommon, other PTCL with abnormal expression of CD20 may occur primarily in the skin.…”

Prevalence of CD20+ cutaneous epitheliotropic T‐cell lymphoma in dogs: a retrospective analysis of 24 cases (2011–2018) in the USA

“…CD79a staining and PAX5 staining were used as controls to differentiate B‐cell infiltration from the CD20 + T lymphocytes. Both CD79a and PAX5 are pan B‐cell markers and have been used previously in dogs and humans to differentiate neoplastic lymphocyte populations …”

“…Another published case study documented cluster of differentiation 3 (CD3) and CD20 co‐expression in cutaneous epitheliotropic lymphoma in a dog for the first time and another study documented CD20 + enteropathy‐associated T‐cell lymphoma in three dogs . CD20 co‐expression also has been investigated as a potential prognostic indicator for human cases of CETCL . CD20 is a predominantly B‐cell marker expressed on B cells prior to differentiation into plasma cells …”

“…CD20 co‐expression also has been investigated as a potential prognostic indicator for human cases of CETCL . CD20 is a predominantly B‐cell marker expressed on B cells prior to differentiation into plasma cells …”