Abstract

Precursor B-cell acute lymphoblastic leukemia (pre-B-ALL) cutis is rare with few cases reported in the literature. We present a pediatric case of pre-B-ALL with cutaneous involvement at initial presentation. A 15-month-old female presented with a 3 cm painless, violaceous annular plaque on the left lower leg of 7 weeks duration. An ultrasound performed 2 weeks earlier showed a non-specific solid lesion with internal vascularity. The child had a history of atopic dermatitis but was otherwise healthy. Punch biopsy showed an unremarkable epidermis and a dense, nodular infiltrate of large, atypical lymphocytes with convoluted nuclear borders and scattered mitotic figures in the dermis. Immunohistochemical analysis showed a majority population of B-lymphocytes which expressed Pax-5, CD79a, BCL-2, and CD10. TdT was expressed in over 80% of B-lymphocytes; CD20 was not expressed. Ki-67 staining showed a very high proliferative index. Kappa and lambda immunostains showed scattered, predominantly lambda-positive plasma cells. In-situ hybridization was negative for EBER1. The findings supported a diagnosis of pre-B-ALL/lymphoma cutis. Bone marrow aspirate, peripheral blood flow cytometry, and cytogenetic analysis confirmed a diagnosis of pre-B-ALL with KMT2A rearrangement. This case, which is unique in its lower extremity presentation, underscores the possibility of pre-B-ALL manifesting in the skin as an initial sign and highlights the importance of timely diagnosis in management of this life-threatening condition.