Mixed phenotypic (T cell/B cell) lymphoblastic lymphoma of synovium, report of the first case with discussion on potential diagnostic pitfalls

Abstract

Mixed- phenotype acute leukaemia (MPAL) is very rare and accounts for less than 4% of acute leukaemia. Most cases of MPAL described in literature, are of T/myeloid or B/myeloid phenotype. MPAL T/B cell lineage is exceptional and occasional cases reported so far, are leukaemia with bone marrow involvement. Our case, on immunophenotyping, exhibited evidence of T and B- Lymphoid lineage. It could be diagnosed neither as MPAL, because the bone marrow was not involved, nor as lymphoblastic lymphoma because of the bi phenotypic expression of both T and B cell antigens. Hence, we reported it as Mixed phenotypic (T cell/B cell) Lymphoblastic Lymphoma. This is the first case, extra medullary as well as extra lymphoid in location, presenting as right elbow synovial lesion. We also discuss the potential diagnostic pitfalls and emphasise the importance of Immunohistochemistry in diagnosis of lymphoblastic lymphomas.