Decrease of 5-hydroxymethylcytosine in primary cutaneous CD4+ small/medium sized pleomorphic T-cell lymphoproliferative disorder

Abstract

Background: Primary cutaneous CD4⁺ small/medium-sized pleomorphic T-Cell lymphoproliferative disorder (PC-SMTLD) has been considered as a controversial dermatological disease that has been included in cutaneous T-cell lymphoma group, presenting most commonly as a solitary nodule and/or plaque with a specific and characteristic head and neck predilection. Due to the considerable overlap between PC-SMTLD and pseudolymphoma (PL), the differential diagnosis is often challenging. Methylation of DNA at position 5 of cytosine, and the subsequent reduction in intracellular 5-hydroxymethylcytosine (5-hmC) levels, is a key epigenetic event in several cancers, including systemic lymphomas. However, it has rarely been studied in cutaneous lymphomas.

Objectives: The authors aimed to explore the role of differential 5-hmC immunostaining as a useful marker to distinguish PC-SMTLD from PL.

Methods: Retrospective case series study with immunohistochemical and immunofluorescence analysis of 5-hmC was performed in PL and PC-SMTLD.

Results: Significant decrease of 5-hmC nuclear staining was observed in PC-SMTLD when compared with PL (p < 0.0001). By semi-quantitative grade integration, there were statistical differences in the final 5-hmC scores in the two study groups. The IF co-staining of 5-hmC with CD4 revealed a decrease of 5-hmC in CD4⁺ lymphocytes of PC-SMTLD.

Study limitations: The small clinical sample size of the study.

Conclusions: The immunorreactivity of 5-hmC in CD4⁺ lymphocytes was highly suggestive of a benign process as PL. Furthermore, the decrease of 5-hmC nuclear staining in PC-SMTLD indicated its lymphoproliferative status and helped to make the differential diagnosis with PL.

Keywords: Cutaneous T-cell lymphoma; DNA methylation; Epigenomics.

Figure 1

Histological Findings of PC-SMTLD. No obvious abnormalities were observed in the epidermis and diffuse lymphoid cell infiltration was observed in the entire dermis. At high magnification, a large number of small to medium sized lymphocytes were seen in the dermis, with mast cells, plasma cells, and eosinophils scattered in the background. (Hematoxylin & eosin, scale bar = 100 μm).

Figure 2

Immunohistochemistry of PC-SMTLD. Case 2. The neoplastic cells strongly express CD3, CD4 and CD7; rarely express CD8, CD10 or CD30, do not express CD56. (IHC, scale bar = 100 μm).

Figure 3

Expression of 5-hmC. primary cutaneous CD4⁺ small/medium sized pleomorphic T-cell lymphoproliferative disorder (PC-SMTLD) and Pseudolymphoma(PL): significant decrease of 5-hmC expression was observed in PC-SMTLD when compared with PL in dermis (Fig. 3A). (****p < 0.0001). (Fig. 3B). The difference in nuclear staining score for 5-hmC was statistically significant with higher scores in the PL group (mean = 2.35, Standard Deviation [SD = 0.50]) when compared to PC-SMTLD (mean = 1.33, SD = 0.47, p = 0.0014) (Fig. 3C). The majority of PL 95% (19/20) cases were in the high expression group (Fig. 3D).

Figure 4

Expression of TET2: No significant difference in TET2 expression were observed in two groups.

Figure 5

Immunofluorescence (IF) co-staining of 5-hmC (green) and CD4 (red) in PC-SMTLD and PL samples: Decrease of 5-hmC in CD4⁺ lymphocytes were observed in PC-SMTLD. DAPI (blue) was used to show cell nucleus.