Treatment of acute promyelocytic (M3) leukemia

Early diagnosis and treatment of acute promyelocytic leukemia (APL), the M3 subtype of acute myeloid leukemia (AML), is important because patients with APL may develop serious blood-clotting or bleeding problems. This used to be treated with blood-thinning medicines, but is less often a problem now that treatment includes drugs like all-trans-retinoic acid (ATRA). Other treatments might include transfusions of platelets or other blood products.

The treatment of most cases of APL differs from usual AML treatment. Initial treatment usually involves an anthracycline chemotherapy drug (daunorubicin or idarubicin) plus the non-chemotherapy drug, all-trans-retinoic acid (ATRA), which is a relative of vitamin A.

This treatment induces remission in about 80% to 90% of patients.

Patients who can't tolerate an anthracycline drug may get ATRA plus another drug called arsenic trioxide (Trisenox). The most serious possible side effect of this drug is a change in heart rhythm.

As with other subtypes of AML, patients with APL then receive post-remission treatment.

Consolidation therapy usually consists of 2 or more courses of chemotherapy (with an anthracycline), usually along with ATRA. Those who can't get an anthracycline usually get ATRA plus arsenic trioxide for several cycles.

Consolidation is often followed by maintenance therapy with ATRA for at least a year. Some doctors may also add low doses of chemotherapy, usually with the drugs 6-mercaptopurine (6-MP) and methotrexate.

The possible side effects from the chemotherapy part of this treatment are generally the same as those of standard AML induction chemotherapy. But both ATRA and arsenic can cause a problem called differentiation syndrome (it used to be called retinoic acid syndrome). Symptoms include breathing problems due to fluid buildup in the lungs, low blood pressure, kidney damage, and severe fluid buildup elsewhere in the body. It can often be treated by stopping the drug for a while and giving a steroid such as dexamethasone.

About 70% to 90% of patients with APL are cured with treatment.