Cutaneous precursor B-cell lymphoblastic lymphoma in 2 adult patients: clinicopathologic and molecular cytogenetic studies with a review of the literature.

BACKGROUND Precursor B-cell lymphoblastic lymphoma (B-LBL) is an uncommon high-grade neoplasm of immature B cells. In contrast to the more common lymphoblastic lymphoma of T-cell lineage, B-LBL can be an extranodal disease, with a propensity to involve skin and bone. Most reported cases of B-LBL in the skin, a rarity in adults, are manifestations of existing systemic disease. OBSERVATIONS We report 2 unusual cases of primary cutaneous B-LBL in adults. Fluorescence in situ hybridization studies, not previously reported in primary cutaneous B-LBL to our knowledge, demonstrated rearrangement of the MLL gene in one patient and possible hyperdiploidy in the other, both reported in precursor acute lymphoblastic leukemia. CONCLUSIONS Review of the literature identified 13 reported cases of B-LBL occurring primarily in the skin, in addition to our 2 cases. Precursor B-cell lymphoblastic lymphoma is more common in children and in young adults, with a tropism for the head and neck region. Histologically, B-LBL must be differentiated from other high-grade lymphoid tumors and small "blue round cell" tumors. Because of the common absence of mature B-cell markers in immunohistochemical studies and the frequent expression of CD99, B-LBL may present a diagnostic challenge. Although there is a suggestion in a limited number of patients that abbreviated therapy may provide long-term disease control, the risk of relapse remains significant, particularly if a patient's condition is misdiagnosed and the patient is treated as having mature B-cell lymphoma. In the absence of prospective studies for this population, patients with B-LBL are treated currently with intensive acute lymphoblastic leukemia regimens.