Cytokeratin Expression in Plasmablastic Lymphoma - a Possible Diagnostic Pitfall in the Routine Work-Up of Tumors

Lymphoma
10/11/2020

Histopathology. 2020 Nov 9. doi: 10.1111/his.14300. Online ahead of print.

ABSTRACT

AIMS: Plasmablastic lymphoma (PBL) is a rare aggressive B-cell lymphoma frequently arising at extranodal sites in the setting of immunosuppression. The diagnosis of PBL is complex, owing to a frequent solid or cohesive growth pattern and often unusual immunophenotype. Several case reports have described the expression of cytokeratins (CK) in PBL introducing a diagnostic pitfall. In the largest series available to date, our goal was to determine the frequency of CK reactivity in PBL.

METHODS AND RESULTS: Using immunohistochemistry in a cohort of 72 PBL, we identified reactivity for CK8/18 in 11/72 cases (15%) and AE1/3 in 6/65 cases (9%), clearly contrasting with a control series of non-PBL aggressive B-cell lymphomas (1/96 diffuse large B-cell lymphomas), as well as with data in the literature describing only occasional CK expression in hematological neoplasms.

CONCLUSIONS: Our data indicate reactivity for CK in a substantial number (15%) of PBL. In view of its particular morphological features and frequent negativity for the common leukocyte antigen and B-cell markers, this feature represents a pitfall in the routine diagnostic work-up of PBL and requires more extensive immunohistochemical and molecular characterization of cases entering the differential diagnosis.