Clusterin expression in cutaneous CD30‐positive lymphoproliferative disorders and their histologic simulants

Background:  Clusterin is a ubiquitous 80 kDa heterodimeric glycoprotein previously shown to be expressed on tumor cells of systemic and, to a lesser extent, primary cutaneous anaplastic large cell lymphoma (PC‐ALCL). Lymphomatoid papulosis (LyP), an important differential diagnosis of ALCL, has been studied for clusterin expression in only a small number of cases. The aim of this study was to compare clusterin immunostaining patterns in LyP and other cutaneous histologic simulants with those of PC‐ALCL. Methods:  Formalin‐fixed, paraffin‐embedded sections of PC‐ALCL (6), LyP (20), mycosis fungoides with large cell transformation (MF‐LCT, 12), pityriasis lichenoides et varioliformis acuta (PLEVA, 12), arthropod bite reaction (ABR, 12) and lymphomatoid reactions (LR, 9) were immunostained for clusterin and evaluated for staining pattern and distribution. All diagnoses were made with clinicopathologic correlation. Results:  Characteristic dot‐like Golgi staining was identified in 10/20 LyP (50%), 4/6 PC‐ALCL (67%) and 9/12 MF‐LCT (75%). Two of 12 PLEVA (17%), 1 of 12 ABR (8%) and 2 of 8 LR (25%) had lymphocytes (< 25%) with diffuse cytoplasmic staining. Dermal dendritic cells stained strongly for clusterin. High background staining occurred in some cases. Conclusion:  Clusterin immunostaining does not reliably distinguish between LyP, PC‐ALCL or MF‐LCT, but could distinguish LyP from its reactive histologic simulants.