Differential NFATc1 Expression in Primary Cutaneous CD4+ Small/Medium-Sized Pleomorphic T-Cell Lymphoma and Other Forms of Cutaneous T-Cell Lymphoma and Pseudolymphoma.

BACKGROUND: Primary cutaneous CD4 small/medium-sized pleomorphic T-cell lymphoma (PCSTCL) has recently emerged as a distinct clinicopathological entity. Because of a considerable degree of overlap with pseudolymphoma, the diagnosis is often challenging. Preliminary studies suggest that nuclear upregulation of calcineurin/nuclear factor of activated T cells (NFAT) may play a role in lymphomagenesis.

DESIGN: 137 cases (70 males and 67 female, mean age = 55) of various forms of cutaneous T-cell and B-cell infiltration were evaluated for NFATc1 expression. The study comprised 18 cases of PCSTCL, 45 cases of mycosis fungoides (MF), 5 cases of lymphomatoid papulosis (LyP), 5 cases of anaplastic large-cell lymphoma (ALCL), 8 cases of other forms of peripheral T-cell lymphoma, not otherwise specified, 12 precursor lesions of MF (ie, cutaneous T-cell dyscrasias), 35 cases of pseudolymphomas, 8 primary cutaneous B-cell lymphoma, and 1 chronic lymphocytic leukemia. The number of cells exhibiting a nuclear stain was counted per 10  high-power field and 2-tailed statistical analysis was used for comparison of nuclear NFATc1 expression between primary PCSTCL and all other groups. A P-value <0.05 was considered to indicate statistical significance.

RESULTS: All cases of PCSTCL showed nuclear staining for NFATc1 (mean = 296 ± 236) with no cases in which an exclusive cytoplasmic stain was observed. The cells exhibiting this staining pattern were oftentimes larger manifesting other features of a follicular helper T-cell phenotype, such as variable positivity for PD1, ICOS, CXCL13, and BCL6. In comparison, an exclusively cytoplasmic stain was observed in 29 cases of MF; in few cases, rare nuclear staining cells were observed averaging less than 10 per high-power field (P = 0.0001). These positive staining cases were not only limited to tumor-stage MF but also encompassed patch- and plaque-stage lesions and follicular variants of MF. The same pattern was observed in cases of T-cell dyscrasia (mean = 3 ± 3, P = 0.0001) and pseudolymphoma (mean = 2 ± 3, P = 0.0001), both revealing a dominant cytoplasmic staining pattern. In pseudolymphomatous folliculitis, a greater extent of nuclear staining for NFATc1 was observed compared with other forms of pseudolymphoma. No significant difference was seen between MF and T-cell dyscrasia or pesudolymphomas excluding pseudolymphotous folliculitis. Anaplastic large-cell lymphoma cases showed an almost exclusive cytoplasmic staining pattern with rare nuclear staining (mean = 55 ± 102, P = 0.0001); similar results were observed in LyP (mean = 17 ± 15, P = 0.004). Cutaneous B-cell lymphomas showed a similar extent of staining as that noted for PCSTCL. The greatest extent of staining was observed in chronic lymphocytic leukemia. A significant difference was noted between the extent of nuclear staining in PCSTCL and other forms of primary cutaneous T-cell lymphoma, type unspecified (mean = 22 ± 43, P = 0.0002), although not between PCSTCL and B-cell lymphoma.

CONCLUSION: NFAT signaling plays a critical role in peripheral T-cell activation after T cell receptor engagement. When assessing T-cell-rich infiltrates where the differential diagnosis is largely between a PCSTCL and pseudolymphoma, a significant degree of nuclear staining of lymphocytes would be more in keeping with a diagnosis of PCSTCL. Upregulation of the NFAT pathway is not a feature of tumor progression in the setting of MF.