Biphenotypic acute leukemia (BAL) is a rare form of acute leukemia, accounting for 1 percent to 5 percent of acute leukemias. Most acute leukemia cases are classified as either acute myeloid leukemia (AML) or acute lymphoblastic leukemia (ALL), based on the types of cells involved. BAL, however, is a subtype of acute leukemia that involves cells of both myeloid and lymphoblastic lineage. BAL may also be called mixed-phenotype acute leukemia (MPAL).

The cause of BAL is unknown. A person can develop the condition at any age, but it is more common in adults than in children. BAL is a unique condition and no treatments have been designed specifically to treat it. Doctors and researchers are working hard to figure out the best treatment for each person living with BAL and to find a cure for this disease.

Causes of Biphenotypic Acute Leukemia

All cancers develop because of genetic mutations that cause cancerous cells to grow out of control. Chromosomes contain genetic material and are found within cells. BAL is often accompanied by a chromosomal rearrangement that causes a shortened chromosome 22, termed the Philadelphia chromosome. People with BAL may also have abnormalities in chromosome 11. There are usually multiple chromosomal rearrangements and genetic mutations in the DNA of people living with BAL. These complex genetic changes are part of what makes BAL difficult to study and treat.

Experts don’t fully understand what causes these changes, and researchers are still working to identify biomarkers that can predict one’s risk of developing BAL. BAL tends to develop suddenly for no known reason. Rarely, people can develop BAL after undergoing chemotherapy or radiation treatments for other cancers. These cases are known as secondary leukemia.

Signs and Symptoms of Biphenotypic Acute Leukemia

BAL can affect B cells and T cells, lymphoid cells that play important roles in the immune system. BAL can also affect myeloid cells, which make red blood cells. In BAL, at least two types of cells have become leukemic — either a combination of B cells and myeloid cells, or a combination of T cells and myeloid cells. In extremely rare cases, it is possible for B cells, T cells, and myeloid cells to all become cancerous.

The effects on these cells mean symptoms of BAL are often similar to symptoms of other leukemias. People with BAL commonly report:

• Fatigue
• Fever
• Bleeding and prolonged healing
• Unusually frequent or severe infections

Thrombocytopenia (low numbers of platelets in the blood) can lead to bruising or decreased ability of blood to clot. A BAL-associated decrease of hematopoietic cells (those that make red blood cells) leads to low numbers of circulating red blood cells, which can lead to anemia.

If cancerous cells gather in other tissues, other symptoms can develop, such as:

• Swollen lymph nodes
• Joint pain
• An enlarged liver
• Swelling of the gums
• An enlarged spleen
• Fluid buildup in the skin, lungs, and abdomen

If cancerous cells are in the central nervous system, vomiting and headaches can result.

Diagnosis of Biphenotypic Acute Leukemia

A correct and quick diagnosis of BAL is very important so that treatment can begin as soon as possible.

The European Group for Immunological Classification of Leukemias and the WHO have set diagnostic criteria for BAL based on cell markers. A sample of blasts (cancerous cells) taken from the bone marrow is required for diagnosis. This procedure typically requires a bone marrow biopsy or aspiration, in which the doctor uses a needle to collect a sample of tissue from the bone marrow, generally taken from the hip.

Testing called flow cytometry is used to perform immunophenotyping, which determines how mature the cancerous cells are and whether they are myeloid or lymphoid. These tests are done using a blood sample. Information on immunophenotype is combined with information on cancer cell morphology (their size and shape) and their genetic background. This information allows doctors to tell the difference between BAL and other forms of acute leukemias.

Treatment for Biphenotypic Acute Leukemia

There is no standard induction chemotherapy (or first type of chemotherapy treatment) for BAL. Typically, doctors will use chemotherapy that has been designed for either AML or ALL.

Chemotherapy

Standard ALL treatment regimens can include chemotherapy combinations called:

• Cerubidine (daunorubicin), Oncovin (vincristine), and prednisone (DVP)
• Cytoxan (cyclophosphamide) with DVP (CDVP)
• L-Asparagine with CDVP

Standard AML treatment regimens include:

• High-dose cytarabine with Novantrone (mitoxantrone)
• Cytarabine with Toposar (etoposide)
• Cytarabine with Cerubidine

Therapy designed to treat ALL tends to have higher initial remission rates than therapy designed to treat AML: In one study involving 10 people with BAL, eight participants underwent chemotherapy. Five achieved complete remission after initial therapy — four from chemotherapy designed to treat ALL, and one from chemotherapy designed to treat AML. Although most people achieved complete remission, relapse rates were very high, and the rate of complete remission after relapse was low. Both treatments have similar long-term survival rates.

Stem Cell Transplantation

Stem cell transplantation is a procedure that may be used after chemotherapy. Through allogeneic stem cell transplantation, a person’s broken-down, less functional cells that were harmed by chemotherapy are replaced with healthy stem cells (cells that make new blood cells) from a matched donor. Treatments for BAL that combine intensive chemotherapy and stem cell transplantation have helped people reach complete remission. However, older people or people living with complicating conditions often find the treatment regimen difficult to endure, so stem cell transplants are generally not recommended for them.

Prognosis for Biphenotypic Acute Leukemia

BAL has a high rate of relapse (returning after treatment), and relapsed disease is often resistant to therapy. As a result, BAL has a poor prognosis (outlook) compared to AML or ALL.

A study involving 100 people living with BAL was done to find out more information about prognosis. Treatment regimens designed for ALL reduced disease in 85 percent of cases. Treatment designed for AML reduced disease in 41 percent of cases. The five-year survival rate was 37 percent, although the overall survival was about 18 months after diagnosis. The presence of certain genetic abnormalities or a very high white blood cell count were indicators of a worse outlook.

Talk With Others Who Understand

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