Immunophenotyping and genotyping are usually helpful in defining cell lineage. However, aberrant immunohistochemical expression is seen in a small proportion of B and T cell lymphomas.1 ,2 Immunohistochemical studies may be supplemented by a molecular search for immunoglobulin heavy (IGH) chain and T cell antigen receptor (TCR) rearrangements. It has been reported that simultaneous rearrangements of both IGH and TCR are not rare and cross-lineage rearrangements are encountered in about 10% of mixed lymphomas.3 These cases may correspond either to dual genotype lymphomas with two distinct monoclonal populations or to bigenotypic lymphomas with IGH and TCR rearrangements in the same cell. We describe an extremely rare case of a patient with lymphoma expressing both B and T cell antigens and showing both IGH and TCR rearrangements.

The patient presented with fever, generalised lymphadenopathy and multiple maculopapular skin eruptions. The patient had a history of erythema nodosum diagnosed 1 year before. Laboratory investigation showed a worsening pancytopenia, hypogammaglobulinaemia with IgG levels of 562 mg/dL, high lactate dehydrogenase (981 IU/L) and β₂-microglobulin 10.7 mg/L (range 0.8–2.4). The anaemia (Hct 28%, Hb=9.5 g/dL) was microcytic with features of anaemia of chronic disease. HIV antibodies, anti-HCV and HBsAg were negative whereas anti-HBs and anti-HBc were positive. CT scans revealed enlarged cervical, mediastinal, hilar, axillary, mesenteric, retroperitoneal, iliac and femoral lymph nodes.

An axillary lymph node biopsy along with bone marrow and skin biopsies were performed. Histological examination revealed complete effacement of lymph node architecture by …