—  SPECIALTY CONFERENCE  —

Hematopathology

Case 2 - Subcutaneous Panniculitis-Like T Cell Lymphoma

Paul J. Kurtin
Mayo Clinic
Rochester, MN


Click on each slide thumbnail image for an enlarged view
Histology
The subcutaneous fat contains foci of necrosis alternating with lobular and septal lymphocytic infiltrates (Figure 1). A bland appearing population of small lymphocytes associated with histiocytes and occasional multinucleated giant cells border the necrotic fat. In the areas remote from the fat necrosis, small and medium sized lymphocytes infiltrate the fat lobules (Figure 2). In these areas many of the lymphocytes are cytologically abnormal with highly irregular hyperchromatic nuclei, inconspicuous nucleoli and sparse pale staining cytoplasm (Figure 3). They circumferentially rim the fat cells and are associated with karyorrhectic nuclear material and histiocytes with angulated, twisted nuclei and variable amounts of clear cytoplasm.


Case 2 - Figure 1 - A mixed population of lymphocytes and histiocytes infiltrates the lobules and septa of the subcutaneous fat. Hematoxylin and eosin, 100X.
Case 2 - Figure 2 - Abnormal medium size lymphocytes and histiocytes are present surrounding the adipocytes. Note the apoptotic debris within some of the macrophages. Hematoxylin and eosin, 200X.
Case 2 - Figure 3 - The abnormal lymphocytes have irregular, hyperchromatic nuclei with inapparent nucleoli, and sparse cytoplasm. They rim the fat spaces and are mixed with macrophages with twisted nuclei, delicate chromatin, single nucleoli and abundant clear cytoplasm. Some of the macrophages contain apoptotic debris. Hematoxylin and eosin, 600X.


Case 2 - Figure 4 - The neoplastic lymphocytes are positive for CD2. Immunoperoxidase stain for CD2, 200X.
Case 2 - Figure 5 - The neoplastic lymphocytes express CD8. Immunoperoxidase stain for CD8, 200X.
Case 2 - Figure 6 - Granzyme B positive lymphoma cells rim the fat spaces and are present between fat cells. Immunoperoxidase stain for granzyme B, 600X.

Immunophenotype
In paraffin section immunoperoxidase stains, the abnormal lymphocytes expressed CD2 (Figure 4), CD3ε, CD5 and CD8 (Figure 5). They were positive for the cytolytic granule proteins granzyme B (Figure 6) and Tia-1 and they expressed the αβ T cell receptor (βF1 positive). They were negative for CD7, CD4 and CD20.

Molecular Genetic Analysis
Using the polymerase chain reaction technique with primers that recognize the T cell receptor gamma chain genes applied to DNA isolated from the paraffin sections of the fat specimen, clonal T cell receptor gene rearrangements were detected. In addition a frozen sample was studied for T cell receptor gene rearrangements using the Southern blot technique. Again, clonal rearrangement bands were detected using probes that recognize the T cell receptor beta chain gene (first and second joining regions).

The morphologic, phenotypic and genetic features are characteristic for subcutaneous panniculitis like T cell lymphoma.

Discussion
Although small series and individual case reports described patients with "panniculitis" who in retrospect had clinical and pathologic features that are now thought to be compatible with subcutaneous panniculitis-like T cell lymphoma (SPTCL), the first description proposing this disorder as a distinctive lymphoma type was published by Gonzales, et al in 1991 [1] . Since then the diagnostic criteria for this disorder have evolved and a clearer picture of this disease as a specific entity has emerged. The World Health Organization (WHO)-European Organization for Research and Treatment of Cancer (EORTC) classification for cutaneous lymphomas now defines this disease as a lymphoma of cytolytic αβ T lymphocytes that primarily involves the subcutaneous tissues and which can be accompanied by a hemophagocytic syndrome [2] . While the original WHO lymphoma classification included cytolytic lymphomas of γδ type within the SPTCL category [3] , sufficient additional studies have now been performed which suggest that γδ T cell lymphomas that involve the subcutaneous tissues may be better grouped with other cutaneous γδ T cell lymphomas as a provisional entity: cutaneous gamma/delta T cell lymphoma.

Clinical Features of SPTCL [4]
SPTCL occurs in both children and elderly adults, but the median age at diagnosis is 42 years. Females are affected slightly more frequently than males (The male to female ratio is 1:1.3). The disease produces tender erythematous subcutaneous nodules that are usually multiple and that ulcerate in approximately 20% of cases. The lower extremities are most frequently involved, followed by the trunk, arms and face. Fever, weight loss, and myalgias occur in approximately 40% of patients and 10% have liver function abnormalities. Anatomic sites other than the subcutaneous tissue are rarely reported to be involved by SPTCL.

All SPTCL case series include subsets of patients who have a hemophagocytic syndrome, characterized by severe systemic symptoms, hepatosplenomegaly and cytopenias. The hemophagocytic syndrome was reported to occur more frequently, but not exclusively in patients with γδ SPTCL. Now that the γδ cases have been excluded from the category of SPTCL, the exact frequency of this complication is uncertain. Proinflammatory cytokines elaborated by the neoplastic cells are thought to activate macrophages at sites remote from those involved by the lymphoma, such as spleen, liver, lymph nodes, and bone marrow and to produce the hemophagocytosis. The single best predictor of adverse outcome in patients with SPTCL is the presence of a hemophagocytic syndrome.

The clinical course of this disease varies. Rarely spontaneous remissions occur. In some patients the disease is indolent with a slow evolution characterized by recurrences and remissions after varyingly intense chemotherapy. In other patients the disease proceeds aggressively from the start with prominent systemic signs and symptoms, liver function test abnormalities, coagulopathy and dissemination to multiple anatomic sites. In this patient group intense chemotherapy with autologous bone marrow transplant has produced clinical remissions. Except for the poor prognosis associated with the hemophagocytic syndrome, it is difficult to predict the clinical course of individual patients. However, increased lactate dehydrogenase levels and neutropenia seem to be associated with more aggressive disease.

Microscopic Features of SPTCL [1, 5, 6, 7, 8]
Fat lobules and to a lesser extend the septa are infiltrated by abnormal lymphocytes that typically rim individual fat cells. The cellular infiltrates can involve the deep reticular dermis, particularly around blood vessels, but if there is any substantial involvement of the mid or upper reticular dermis or the papillary dermis a disease other than SPTCL should be considered.

The cytologic features of the lymphocytes vary from case to case and between different lesions biopsied at different times during the course of the disease. They are usually small to medium sized with hyperchromatic nuclei, highly irregular nuclear contours, absent nucleoli and small amounts of pale staining cytoplasm. Some cases contain larger lymphoid cells in varying proportions with more dispersed chromatin and distinct nucleoli.

Karyorrhectic nuclear debris is found amid the neoplastic lymphocytes in most cases and is associated with peculiar macrophages with twisted, angulated nuclei. These cells can be confused with the neoplastic lymphocytes. However, they have more dispersed chromatin compared to the darkly staining nuclei of the lymphoma cells and the histiocytes have more abundant clear or foamy cytoplasm. Macrophages with hemophagocytosis can also be mixed with the lymphoma cells. The presence of hemophagocytosis within the tumor itself does not necessarily predict the presence of a systemic hemophagocytic syndrome.

The adipose tissue involved by SPTCL frequently shows areas of necrosis. As in the presented case, necrotic zones are often surrounded by a granuloma-like tissue reactions that can obscure the presence of the lymphoma. In these instances, one must examine the fat away from the necrotic areas to find the characteristic lymphomatous infiltrates. Angiocentric and angiodestructive lesions are not usually observed in SPTCL, but venules in the involved fat often show transmural infiltrates of the neoplastic lymphocytes without obliteration of the vascular lumens. Typically, plasma cells and reactive germinal centers are not part of the histologic features of SPTCL.

Phenotypic Features of SPTCL [5, 7, 8, 9]
In most cases, the lymphoma cells express CD3, CD8, Tia-1, granzyme B and perforin. To fulfill the new WHO/EORTC definition of the disorder, the tumor cells should be shown to be αβ T cells. This is most readily accomplished by staining them for βF1 by paraffin section immunohistochemistry. In addition they exhibit variable reactivity for CD2, CD3, CD5 and CD7. They are usually CD4 and CD56 negative. While it is characteristic for γδ T cells to lack staining for CD5, CD4 and CD8, there are rare cases of αβ SPTCL that are CD5 negative or both CD4 and CD8 negative. Earlier reports of SPTCL suggest that they are CD4 positive in a rather substantial fraction of cases, but those studies were based on frozen section immunohistochemistry in which morphology is less than optimal. It is likely that the abundant CD4 positive macrophages in the lesions were mistaken for the malignant lymphocytes in these reports.

The cells of SPTCL are invariably negative for Epstein-Barr virus related antigens, such as latent membrane protein-1. They are also negative for Epstein Barr virus encoded RNA (EBER) by in situ hybridization.

Genetic features of SPTCL
Clonal T cell gene rearrangements can demonstrated by either the polymerase chain reaction technique applied to frozen or paraffin embedded tissue or by the Southern blot technique applied to frozen tissue samples of a large fraction of all SPTCL cases. In our experience, cases that do not show clonal T cell rearrangements are inadequately sampled to include the diagnostic lesion.

There are no specific chromosomal abnormalities that have been detected in this disorder.

Differential Diagnosis

Panniculitis. The panniculitides are a complex group of diseases. Even a superficial treatment of them is outside the scope of this handout. For a comprehensive review the reader is referred to a recent article [10] that provides an excellent overview of this topic.

In general lupus panniculitis is the entity that most resembles SPTCL. In both there is a prominent lymphocytic infiltrate of fat lobules. In contrast to SPTCL, though, lupus panniculitis often contains reactive B cell follicles and plasma cells. The cytology of the lymphocytes is bland and there is less prominent rimming of fat cells by the infiltrating lymphocytes. The epidermis and superficial dermis of lupus panniculitis cases will also show the typical features of lupus erythematosus in 50% of cases (vacuolization at the dermal-epidermal infiltrate, lymphocytic infiltrates centered on cutaneous appendages and associated with follicular plugging, etc.} Phenotypically, lupus panniculitis is composed of mixtures of CD4 and CD8 positive T cells. Cytolytic lymphocytes rimming fat are generally not observed. Clonal T cell rearrangements are generally not observed in lupus panniculitis, but at least one manuscript suggests that they are not infrequently identified in that disorder. Finally, most, but not all patients with lupus panniculitis have overt clinical manifestations of systemic lupus erythematosus. It is likely that cases termed "lupus profundus" in patients who do not have the clinical features of systemic lupus erythematosus include some clinically indolent cases of SPTCL [11] and additional studies determining the relationship between these two types of lymphocytic infiltrates in the subcutis are warranted.
Cutaneous γδ T cell lymphoma. [12, 13, 14] Those cases previously considered to be SPTCL of γδ type are now provisionally linked with other skin-based γδ T cell lymphomas in the WHO/EORTC classification. Typically, those that involve the subcutaneous fat will show greater involvement of the mid and superficial dermis than αβ SPTCL cases. Rimming of fat cells, the cytology of the neoplastic lymphocytes, and the presence of apoptosis and a histiocytic infiltrate are features common to both entities. Characteristically, γδ T cell lymphomas express CD2, CD3 and often CD56 and they are negative for CD5, CD4 and CD8. They are Tia-1 and Granzyme B positive. In paraffin section immunoperoxidase stains, they lack immunoreactity for βF1 and by frozen section immunohistochemistry the neoplastic cells can be shown to express the γδ T cell receptor. The reason to separate these cases from SPTCL is their involvement of the dermis, higher frequency of systemic hemophagocytosis, more frequent involvement of mucosal sites and their uniformly aggressive clinical course.
NK/T cell lymphoma, nasal type (NK/TCL} [15, 16, 17] . NK/TCL typically presents in the nose and paranasal sinuses, but primary cutaneous cases have been described in the literature. Typically, there is involvement of the adipose tissue and dermis. Prominent angiocentric, angioinvasive and angiodestructive lesions associated with broad zones of necrosis are characteristically seen in these tumors. The abnormal lymphocytes span a spectrum from small to large and usually contain highly irregular, hyperchromatic nuclei with absent or small nucleoli. Most cases are NK cell lineage. Thus they are positive for CD2, CD7 and CD56. Using paraffin section immunohistochemistry, they are positive for CD3ε, but they lack the fully assembled T cell receptor and so they are negative for CD3 using antibodies that require a complete T cell receptor complex for immunoreactivity. Typically, they lack staining for CD5, CD4 and CD8 and they do not rearrange T cell receptor genes and as such one cannot demonstrate clonal T cell receptor gene rearrangements in these lesions. Finally, virtually all cases are associated with Epstein-Barr virus which can be readily demonstrated in the tumor cells by in situ hybridization for Epstein-Barr virus encoded RNA (EBER).
So called blastic NK-cell lymphoma/leukemia [18, 19, 20] . This is a heterogeneous disorder which is usually not truly natural killer cell lineage. Most cases are now thought to be neoplasms of probable dendritic cell precursors. Patients present with cutaneous tumors with or without lymphadenopathy. Blood and bone marrow are frequently involved. The neoplastic cells haphazardly infiltrate dermis and subcutis and have blast-like characteristics: medium size nuclei, irregular nuclear borders, delicate stippled chromatin, small or inconspicuous nucleoli and sparse cytoplasm. They are CD56 positive and often express CD4 and CD43. Most other markers of myeloid, T cell or NK cell lineage are not found on the tumor cells. CD123, a marker of dendritic cell precursors has been shown to be positive in some of the cases. T cell receptor genes are germline and no specific karyotypic abnormalities have been associated with this disorder. Regardless of its lineage, this is a very aggressive neoplasm that is clinically and pathologically difficult to distinguish from acute myeloid leukemia.
Enteropathy-type T cell lymphoma. [21] Rare cases of enteropathy type T cell lymphoma have been described that involve the subcutaneous fat in an identical pattern as SPTCL. Based solely on morphology or phenotype and molecular genetic studies, these cases are almost impossible to distinguish from SPTCL. Therefore it would seem prudent to exclude enteropathy type T cell lymphoma and celiac disease in all patients with SPTCL by clinical evaluation.
Diffuse large B cell lymphoma exhibiting an angiodestructive growth pattern and associated with Epstein-Barr virus. [22, 24] This lesion frequently involves subcutaneous fat where it can be primary or a site of dissemination from a primary pulmonary lesion. An angiocentric, angiodestructive growth pattern with widespread necrosis is centered on the fat and the deep dermis. At the borders of the necrosis and the viable tissue, one observes large lymphoid cells with vesicular nuclei, prominent nucleoli and fairly abundant cytoplasm. These are the neoplastic lymphocytes. They are CD20 positive, lack immunoreactivity for T cell lineage antigens and are uniformly positive for Epstein-Barr virus using in situ hybridization. They are mixed with variable numbers of small bland T cells and macrophages. Some examples of post transplant lymphoproliferative disorders and the lymphoproliferative lesions associated with methotrexate therapy for rheumatoid arthritis can have the identical morphology and immunophenotype of lymphomatoid granulomatosis. Therefore whenever the diagnosis of lymphomatoid granulomatosis is considered one should query the clinician about the possibility that the patient might have had a transplant or could be receiving immunosuppression (usually methotrexate) for rheumatoid arthritis

References

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