LY14 Diagnostic challenges in cutaneous lymphomas: the importance of multisite biopsy and challenges with clonality interpretation

Abstract A 70-year-old woman developed a swelling on the left upper arm, followed by widespread tender nodules over the trunk and limbs. Apart from a recent ‘sore throat’, she has no relevant medical history. She attended accident and emergency, received oral antibiotics and prednisolone empirically, and was referred to dermatology. An incisional biopsy of the left arm demonstrated a dermal and subcutaneous infiltrate of small-to-medium-sized lymphoid cells in addition to a larger immunoblast-like and Hodgkin-like cell infiltrate with plasma cells. The larger immunoblast-like cells were positive for B-lymphoid markers and Epstein–Barr virus (EBV). The smaller T-lymphoid population was positive for T-follicular helper markers. T- and B-cell clones were detected, with no double- or triple-hit genetic rearrangements identified. A provisional diagnosis of cutaneous EBV-positive diffuse large B-cell lymphoma was favoured. A skin biopsy from a nodule on the left thigh showed similar histological findings. Positron ­emission tomography–computed tomography staging demonstrated scattered skin lesions, the most avid on the right thigh, and avid right inguinal lymph nodes. Nodal core biopsies showed similar features to the skin biopsy; however, the population was predominantly T-lymphoid cells. An identical T-cell clone was noted, and TET2 and DNMT3A mutations. Thus, a final diagnosis on review of all specimens was made of a nodal T-follicular helper cell lymphoma, angioimmunoblastic type (nTFHL-AI). Due to worsening symptoms, the patient was commenced on systemic treatment. A complete metabolic response was achieved after two cycles. nTFHL-AI is a rare, aggressive T-cell lymphoma associated with profound immune dysregulation. Secondary B-cell lymphoproliferation, including EBV-driven B-cell clonal populations and, rarely, secondary cutaneous B-cell lymphomas may occur. However the latter is seen with iatrogenic immunosuppression. This may complicate the diagnostic process and cloud the underlying T-cell lymphoma. This case illustrates the diagnostic complexity and importance of obtaining tissue samples from multiple sites in unusual presentations and the challenge when dual clonality is noted.