November 2021 – Hematopathology

Primary cutaneous gamma delta T-cell lymphoma

The clinical picture with the provided microscopic findings are highly suggestive of cutaneous lymphoproliferative disease. Diagnosis of a cutaneous T-cell lymphoma requires the presence of cytologically atypical T-cells, which often show an aberrant immunophenotype, sometimes requiring genetic corroboration to demonstrate clonality. 

Morphologically, this case shows significant atypia. The neoplastic lymphoid cells are monomorphic, intermediate-sized, and have irregular nuclear contours. These cells infiltrate subcutaneous tissue and deep dermis and show adipocyte rimming (Figure B) and angiodestruction (Figure C). This pattern of lobular, panniculitis-like growth is typical for this lymphoma.

Immunophenotypically, our case shows partial expression of CD5, very dim CD7, partial CD56, dual CD4/CD8 negativity, and strong uniform expression of TCR delta with co-expression of cytotoxic markers TIA-1 and granzyme B. In combination, the above findings best support a diagnosis of primary cutaneous gamma delta T cell lymphoma.

In most cases, this rare T-cell cutaneous lymphoma has an aggressive clinical course with frequent mucosal and extracutaneous dissemination and the risk of hemophagocytic lymphohistiocytosis. Cases are often CD4-/CD8- but can occasionally express CD8. The 5-year overall survival is poor at 11% to 33%. 

• Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare adipotropic T-cell lymphoma with a CD8 positive cytotoxic αβ immunophenotype that infiltrates the subcutaneous tissue preferentially. Cases do not express TCR delta. The overall prognosis is generally favorable.  
  
• Primary cutaneous anaplastic large-cell lymphoma is an aggressive cutaneous lymphoma that consists of large cells exhibiting anaplastic, pleomorphic or immunoblastic morphology. Epidermotropism may be present, particularly in cases positive for DUSP22-IRF4 rearrangement. Cells should have strong CD30 expression, typically express CD4 and TCR BF1, and lack adipocyte rimming.
  
• Lupus panniculitis is an autoimmune lobular lymphocytic panniculitis. The infiltrate consists of lymphocytes with no cytologic atypia, should show no adipocyte rimming, and often shows admixed plasma cells and histiocytes. The lymphocytes are typically negative for TCR delta. Additionally, there should be clinical and/or laboratory evidence of autoimmune disease, which was not provided in this case.

References

1. Swerdlow SH, Campo E, Harris NL, et al, eds. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. Lyon, France: International Agency for Research on Cancer; 2017.
2. Guitart J, Weisenburger DD, Subtil A, et al. Cutaneous γδ T-cell lymphomas: a spectrum of presentations with overlap with other cytotoxic lymphomas. Am J Surg Pathol. 2012;36(11):1656-1665. doi:10.1097/PAS.0b013e31826a5038