![]() ![]() Results of several studies suggest that, compared with the more common precursor T-cell lymphoblastic lymphoma, B-LBL may have a lower percentage of leukemia development but a predilection for extranodal sites, including the skin and bone. ![]() ![]() 12 In approximately 75% of the patients, the lymphoma involved the skin, bone, and lymph nodes. In a retrospective review of 109 cases of B-LBL, 64% of the patients were younger than 18 years. Findings in some small series 2, 11 suggest that B-LBL is more common in female subjects, but other authors 1, 10 do not confirm the predilection. Many reported cases of B-LBL are in the pediatric population. The natural history of B-LBL is not well defined, and molecular studies are generally lacking because the literature is limited to small series and case reports. Some authors believe that B-LBL is distinct from acute leukemia because the lymphoma may remain localized without leukemic dissemination. 9 Clinically, they are arbitrarily distinguished by the extent of bone marrow and peripheral blood involvement. Precursor B-cell lymphomas are generally grouped with precursor B-cell lymphoblastic leukemias in the World Health Organization classification of tumors of hematopoietic and lymphoid tissue because of their morphologic and immunophenotypic similarities. 7 B-cell lymphoblastic lymphoma is included in World Health Organization Classification of Tumours: Pathology and Genetics of Skin Tumors 8 as a secondary tumor involving the skin. 1 - 6 Primary cutaneous B-LBL is not included in the current World Health Organization–European Organization for Research and Treatment of Cancer cutaneous lymphoma classification. Most cases reported in the published literature represent cutaneous involvement by existing systemic precursor B-cell lymphoblastic lymphoma or leukemia rather than primary cutaneous disease. Primary cutaneous precursor B-cell lymphoblastic lymphoma (B-LBL) is a rare disease. In the absence of prospective studies for this population, patients with B-LBL are treated currently with intensive acute lymphoblastic leukemia regimens. 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. 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. Histologically, B-LBL must be differentiated from other high-grade lymphoid tumors and small “blue round cell” tumors. Precursor B-cell lymphoblastic lymphoma is more common in children and in young adults, with a tropism for the head and neck region. ![]() 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.Ĭonclusions Review of the literature identified 13 reported cases of B-LBL occurring primarily in the skin, in addition to our 2 cases. Observations We report 2 unusual cases of primary cutaneous B-LBL in adults. Most reported cases of B-LBL in the skin, a rarity in adults, are manifestations of existing systemic disease. 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.
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