International Journal of Hematology and Oncology 2018, Vol 28, Num 2 Page(s): 069-073
The Aberrant Expression of Cytokeratin in Plasma Cell Neoplasm

Hiroaki SUZUKI1, Katsushige YAMASHIRO1, Mitsutoshi KUROSAWA2

1National Hospital Organization Hokkaido Cancer Center, Division of Diagnostic Pathology, JAPAN
2National Hospital Organization Hokkaido Cancer Center, Division of Hematology, Sapporo, JAPAN

Keywords: Cytokeratin, Keratin, Myeloma, Immunohistochemistry, Plasma cell, CK8, CK18, CAM5.2
It is known that cytokeratin (CK) is aberrantly expressed in a subset of plasma cell myelomas. We investigated the expression of CK (CAM5.2, AE1/AE3) in fifty consecutive cases of plasma cell neoplasms (plasma cell myeloma, n=43; solitary plasmacytoma of bone, n= 7). Seven (plasma cell myeloma, n= 5; solitary plasmacytoma of bone, n= 2) of the 50 cases were positive for CK (CAM5.2: 7/50, AE1/AE3: 0/50). The seven cases also expressed CK7 (2/7), CK8 (3/7) and CK18 (7/7) with varying intensity. One case was positive (>10%) for both CK8 and CK18 and two cases weakly expressed both CK8 and CK18 (≤10%). CK8 and CK18 are expression partners and are known to form heteropolymeric filament in cells, suggesting that heteropolymeric filament is formed in a subset of plasma cells in myeloma. On the other hand, the seven cases expressed both type I cytokeratin (CK18) and type II cytokeratin (CAM5.2). CAM5.2 primarily reacts with CK8 and to a lesser extent with CK7. Although the CK8 antibody that was used only reacted with 3 of the 7 cases, it is likely that all 7 cases expressed both CK8 and CK18. The follow-up survival data did not show a significant difference between the CAM5.2-positive group and the CAM5.2-negative group.