en Adults Hematology & Oncology Adults Hematology & Oncology گزارش مورد Case report <div style="text-align: justify;"><span style="line-height:2;"><span style="font-family:Arial;"><span style="font-size:14px;">Although acute leukemia commonly relapses in adults, the conversion of leukemic cell lineage (lymphoid or myeloid) upon relapse has rarely taken place. &ldquo;Lineage switch&rdquo; is a term widely used to define the leukemic lineage transformation as assessed by morphology, cytochemistry, and immunophenotyping from diagnosis to relapse. In most lineage switch cases, B-cell lymphoblastic leukemia/lymphoma relapses as acute myeloid leukemia or vice versa. Here, we report an exceedingly rare case of T-cell acute lymphoblastic leukemia relapsing as mixed-phenotype acute leukemia.</span></span></span></div> Acute lymphoblastic leukemia (ALL), Lineage switch, Mixed-phenotype acute leukemias (MPALs), Acute bilineage leukemia 22 25 http://ijbc.ir/browse.php?a_code=A-10-583-1&slc_lang=en&sid=1 Valiollah Mehrzad 10031947532846009163 10031947532846009163 No Hematology Division of Internal Medicine Department, Isfahan University of Medical Sciences, Isfahan, Iran Pardis Nematollahi 10031947532846009164 10031947532846009164 Yes Pathology Department, OMID Professional Hospital, Isfahan University of Medical Science Anahita Emami 10031947532846009165 10031947532846009165 No Hematology Division of Internal Medicine Department, Isfahan University of Medical Sciences, Isfahan, Iran Sayyideh Forough Hosseini drhosseini.forough@gmail.com 10031947532846009166 10031947532846009166 No Hematology Division of Internal Medicine Department, Isfahan University of Medical Sciences, Isfahan, Iran