Abstract

B-cell lymphoblastic leukemia/lymphoma (B-ALL/LBL) is a high-grade neoplasm of immature B-lineage. B-ALL usually involves the bone marrow and peripheral blood, while B-LBL occurs at extramedullary sites with a predilection for the skin, soft tissue, bone, central nervous system, and lymph nodes. Mixed B-ALL/LBL occurs in 10% of cases, and a subset of cases can present with cutaneous involvement. B-LBL can be diagnostically challenging, especially in the absence of simultaneous medullary involvement. Herein, we discuss a case of a 23-year-old male, without significant medical history, who presented with rapidly growing cutaneous nodules on his face, progressing over the period of two months, to his scalp, chest, and upper back. A biopsy from his upper back showed a superficial and deep, dense, monomorphic dermal inflammatory infiltrate composed of small to medium-sized cells with a high N:C ratio. Immunohistochemistry showed diffuse infiltration by blasts positive for B-cell markers (CD19, CD79a, and PAX5) and markers of immaturity (CD10, CD34, and TdT), consistent with B-LBL.  A subsequent bone marrow biopsy demonstrated B-ALL with 30-40% marrow involvement. In conclusion, LBL is rare, accounting for 2% of lymphomas. B-LBL represents 10% of all LBL cases. Cutaneous involvement can occur in a third of cases and presents only a few months before diagnosis.  It can present a diagnostic challenge given the wide range of differential diagnoses (T-LBL, Burkitt lymphoma, myeloid leukemia in blast phase, and small round blue cell tumors e.g. Ewing sarcoma/PNET). Awareness of this entity and its immunophenotype guides us towards the correct diagnosis.