Abstract

Primary cutaneous gamma-delta T-cell lymphoma (PCGDTCL) is a rare and aggressive cutaneous malignancy that frequently spreads to mucosa and extra-nodal sites. PCGDTCL has a high mortality rate, underscoring the need for timely diagnosis. We report a case of PCGDTCL with aberrant B-cell markers, an exceptionally rare event that can confound diagnosis. A 79-year-old male presented with a four-month history of growing nodules on the right posterior calf. The patient denied constitutional symptoms. CT imaging demonstrated two soft tissue masses within the subcutaneous fat with the largest measuring 4.5 * 4.5 * 2.0 cm. Both nodules showed fluorodeoxyglucose (FDG) avidity on FDG PET/CT imaging. A punch biopsy of the large nodule demonstrated a dense, malignant lymphoid infiltrate extending to the deep dermis without epidermotropism. The infiltrate was composed of medium to large cells with irregular nuclear contours, mitoses, and prominent nucleoli. The lesional cells stained positive with CD3, TCR delta and cytotoxic markers (TIA1 and granzyme B), with variable expression of CD7. CD4, CD5, CD8, TCR alpha, TCR beta, CD30, and EBER in-situ hybridization were negative, whereas CD20 and PAX5 highlighted infrequent background B cells. CD56 was positive in scattered cells and CD30 showed rare positivity. Flow cytometric analysis of tissue showed an abnormal T-cell population with B-cell markers (CD79a and CD19) and no evidence of B-cell lymphoma or leukemia. Based on these findings, additional immunostains showed diffuse expression of CD79a and CD19. The findings were consistent with PCGDTCL with aberrant B-cell markers. Although very rare, expression of B cell markers have been described in T-cell lymphomas. To the best of our knowledge, a formal diagnosis of PCGDTCL with aberrant B-cell markers has not been reported. Dermatopathologists should be aware of this aberrant expression to avoid misclassification with potential significant repercussions.

Financial Disclosure:
No current or relevant financial relationships exist.