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Primary cutaneous peripheral T-cell lymphomas (PTCL) include the provisional entity cutaneous CD4-positive small/medium-sized pleomorphic T-cell lymphoma (PCSM-TCL). PCSM-TCL has been shown to express the proteins programmed death-1 (PD-1), BCL6, and CXCL13. PD-1 regulates cellular immune response and is believed to be instrumental in the development of PCSM-TCL. The molecule is also currently a target for immunotherapy in melanoma (see JW Dermatol Apr 20 2012). These authors evaluated whether PD-1 usefully discriminates PCSM-TCL from cutaneous TCLs.
The researchers compared samples from 26 PCSM-TCL patients with 52 biopsies from patients with other CTCLs. All cases were stained for PD-1; if positive for this marker, the samples were stained with antibodies against BCL6, CXCL13, and CD10 to determine if there was a relationship with follicular helper T (TFH) cells. All 26 PCSM-TCL/pseudo-T-cell lymphoma cases reacted with PD-1, BCL6, and CXCL13, but not with CD10. PD-1 was seen in only 2 of 21 cases of mycosis fungoides and 2 of 16 cases of cutaneous peripheral T-cell lymphoma, unspecified. Staining was negative in all 4 cases of aggressive epidermotropic cytotoxic CD8+CTCL and all 11 cases of CD30+ lymphoproliferative disease.
Cetinözman F et al. Expression of programmed death-1 in primary cutaneous CD4-positive small/medium-sized pleomorphic T-cell lymphoma, cutaneous pseudo-T-cell lymphoma, and other types of cutaneous T-cell lymphoma. Am J Surg Pathol 2012 Jan; 36:109.
Comment
PCSM-TCLs are characterized by single or few nodules or plaques of the face or upper trunk. A few large T cells may be present but represent <30% of the process. Other cells (reactive CD8+ T cells, histiocytes, plasma cells, eosinophils) are also noted. Clinical and pathologic presentations of PCSM-TCL overlap with the entity called cutaneous pseudo-T-cell lymphoma. The presence of a clone and loss of pan-T-cell antigens point to PCSM-TCL, but distinguishing features are blurry. PCSM-TCL and pseudo-T-cell lymphoma share a point of origin in the follicular helper T cell. We need to clarify whether two names are necessary for what appears to be one disease. Although the designation is under debate, the data point to a low-grade process with excellent prognosis. The relevant clinical need is to differentiate between PCSM-TCL and other CTCLs. PD-1 is typically detected in PCSM-TCL and rarely in other CTCLs — a practical finding that can prevent unnecessarily aggressive treatment.