LY25 Primary cutaneous diffuse large B-cell lymphoma, leg type presenting as rapidly enlarging nodules on the calf

Abstract

Primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL-LT), is an aggressive lymphoma most commonly affecting the lower legs of older adults. It presents with rapidly enlarging nodules and carries a poorer prognosis than other cutaneous B-cell lymphomas. Early recognition and differentiation from systemic diffuse large B-cell lymphoma involving the leg are essential to guide management. A patient presented with a 4–6-week history of new nodules on the right calf. The first lesion appeared laterally, followed by two adjacent nodules coalescing to form a nodular plaque. The patient was asymptomatic, reporting no B symptoms. Examination revealed two firm, raised, indurated nodules measuring approximately 5 cm. Two 6-mm punch biopsies from the right lateral and posterior calf confirmed aggressive large B-cell lymphoma with features consistent with leg-type lymphoma. Staging positron emission tomography (PET) scan showed intensely avid multifocal uptake within the right lower limb and right inguinal lymph nodes, corresponding to stage II–IV disease. The patient has commenced Pola-R-CHP chemotherapy (polatuzumab vedotin, rituximab, cyclophosphamide, doxorubicin, prednisone), noting that R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisolone) remains the standard first-line treatment. Radiotherapy may be considered for residual or localized disease depending on treatment response. Close multidisciplinary follow-up is essential due to high recurrence rates and overall poorer prognosis compared with other cutaneous B-cell lymphomas. Differentiating primary cutaneous disease from systemic DLBCL involving the leg is critical, as prognosis and management differ. Histologically, lesions are typically CD20+ Bcl-2+ MUM1+, with a high proliferation index. This case demonstrated CD10− staining, positive MUM1 and the absence of follicles. Rapidly enlarging nodules should prompt early biopsy and staging with PET–computed tomography to differentiate primary cutaneous from systemic disease, as this significantly influences treatment planning and prognosis. This case emphasizes the need for prompt diagnosis, thorough staging and multidisciplinary management in PCDLBCL-LT. Awareness of its aggressive nature and high recurrence risk supports early intervention and careful long-term follow-up.