February 2009
Written by Ahren C. Rittershaus, MD, 4th year resident in Pathology at the Medical University of South Carolina, Charleston, South Carolina.

Diagnosis
Subcutaneous panniculitis-like T-cell lymphoma, involving both cutaneous and mesenteric adipose tissue.

Submitting Pathologist
William Poston, Jr. MD, Presbyterian Healthcare, Charlotte, NC.

Case History
The patient is a 51 year old male who presented with a feeling of increasing abdominal fullness. CT scan showed an ill-defined mesenteric mass. A laparoscopic biopsy of the mesentery was taken. While closing, the surgeon noticed a firm area on the skin overlying the abdomen and obtained a biopsy.

Microscopy
Low magnification examination of the mesenteric biopsies shows nodular areas of increased cellularity. The low power view of the skin demonstrates similar areas of increased cellularity, though they are less prominent than in the mesentery. These areas are predominantly restricted to the lobules and spare the septa for the most part. The overlying dermis and epidermis are uninvolved (See Figure 1).

On high power, the skin shows atypical, variably-sized cells rimming adipocytes. In addition to the large cells, prominent mixed inflammation is present, including plasma cells and histiocytes, which could lead to a misdiagnosis of benign lobular panniculitis. (see Figure 2).
The cells rimming the adipocytes are CD3+, CD8+, CD4-, CD56- cytotoxic T-cells. A Ki-67 stain highlights the large, atypical, proliferating nuclei of the neoplastic cells (see Figure 3).

Discussion
Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare disease, described first in 1991 by Gonzalez et al., and is now somewhat more stringently defined as being of alpha-beta T-cell type (1,2). The prognosis is largely influenced by the presence or absence of hemophagocytic syndrome (HPS), which occurs in the setting of SPTCL in 17% of cases. If HPS is present, the disease has a relatively aggressive course with a 5-year survival rate of 46%. In the absence of HPS, the prognosis of SPTCL is excellent, with a 5-year survival rate of 91%.

Interestingly, there was no evidence of a clonal T-cell receptor rearrangement in the skin, however analysis of the mesentery demonstrated a clonal T-cell population with primers for the T- gamma receptor gene. It has been reported that up to 20% of subcutaneous panniculitis-like T-cell lymphomas do not have detectable clonally rearranged T-cell receptors, showing that this finding is not required for diagnosis.

An important disease which needs to be ruled out in the course of diagnosing SPTCL is primary cutaneous Gamma-Delta T-Cell lymphoma (PCGD-TCL), which was recently separated from SPTCL in the new WHO classification (3). By immunophenotype PCGD-TCL is CD3+, CD8-, C56+, is more often associated with HPS, dissemination, and with dermal/epidermal involvement and ulceration, and has a more aggressive course with a 5 year survival rate of only 11%.

This appears to be the first case reported of mesenteric involvement by SPTCL, and therefore the prognostic impact of this finding is unknown.

References

1. Gallardo F, Pujol RM.
   Subcutaneous Panniculitis-Like T-Cell Lymphoma and Other Primary Cutaneous Lymphomas with Prominent Subcutaneous Tissue Involvement. Dermatol Clin. 2008; 26: 529-540. More online »
2. Willemze R, Jansen PM, Cerroni L, Berti E, et al.
   Subcutaneous Panniculitis-Like T-Cell Lymphoma: Definition, Classification, and Prognostic Factors: An EORTC Cutaneous Lymphoma Group Study of 83 Cases. Blood. 2008; 111(2): 838-845. More online »
3. Jaffe ES, Gaulard P, Ralfkiaer E, Cerroni L, Meijer CJLM.
   Subcutaneous Panniculitis-Like T-Cell Lymphoma. In World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues 4th edition. Swerdlow SH, Campo E, Harris NL, et al, editors, 2008, IARC Press, Lyon.

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