Summary

Acute promyelocytic leukemia is defined by a characteristic morphology (AML FAB M3/M3v), by the specific translocation t(15;17) and its molecular correlates (PML/RARa and RARa/PML). Thereby it can be separated from all other forms of acute leukemia.

By all-trans retinoic acid in combination with chemotherapy cure rates of 70 to 80% can be reached. On average, about 10% of patients still die in the early phase of the treatment and about 20 to 30% relapse. Molecular monitoring of the minimal residual disease (MRD) by qualitative nested RT-PCR and quantitative REAL-time PCR of PML/RARa allows to follow the individual kinetics of MRD and to identify patients with an imminent hematological relapse.

A standardized treatment for patients with relapsed APL has not yet been established. With arsenic trioxide (ATO) monotherapy remission rates over 80% were achieved and long-lasting molecular remissions are described. The drug was mostly well tolerated. ATO exerts a dose dependent dual effect on APL blasts, apoptosis in higher and partial differentiation in lower concentrations. ATO was also successfully administered before allogeneic and autologous transplantation. ATO is approved for the treatment of relapsed and refractory APL in Europe and in the USA.

In the present protocol, ATO is given for remission induction:

1. in patients with hematological or molecular first or subsequent relapse of APL and
2. in patients who do not reach a hematological or molecular remission after first line therapy.

Induction therapy with ATO is the mandatory part of the protocol.

After remission induction, there are several options for postremission therapy. Factors which have influence on the treatment decision in the individual case are:

1. the eligibility for allogeneic transplantation
2. the eligibility for autologous transplantation
3. the presence or absence of contraindications against intensive chemotherapy
4. the PCR status after induction and during follow up (RT-PCR of PML/RARa, sensitivity 10-4)

A mandatory form of post-remission therapy is not defined in the protocol. Data and outcomes of any post-remission therapy should be documented in order to collect data of treatment after ATO.

The following stratification of post-remission therapy can be performed according to the decision of the treating physician:

Patients with a HLA-compatible donor who are suitable for allogeneic stem cell transplantation should be transplanted. In patients with a positive PCR one cycle of intensive chemotherapy (HAM) before transplantation should be considered and patients with a negative result are immediately transplanted without preceding chemotherapy. In patients who do not qualify for allogeneic, but for autologous transplantation, the intensity of the chemotherapy (Ara-C dose of the HAM cycle) is scheduled according to the PCR status after ATO and to the patient's age. In patients under 60 years, the recommended single Ara-C dose is scheduled to 3 g/m² in case of a positive PCR result and to 1 g/m² in case of a negative PCR result after ATO. In all patients aged over 60 years, the Ara-C dose should be uniformly reduced to 1 g/m² independent of the PCR status. Patients who are not eligible for allogeneic or autologous transplantation (too old, no stem cells collected, PCR positive stem cell transplant, contraindications against intensive chemotherapy) receive three further cycles with ATO and ATRA. The group of patients not qualifying for autologous transplantation, but without contraindications against intensive chemotherapy should receive an age adapted HAM, whenever a positive PCR persists or reappears after the three maintenance cycles of ATO. A close monitoring of the PCR of PML/RARa after each treatment cycle is part of the protocol.

The main objective of the protocol is to take advantage of the expected low toxicity of ATO and to keep the part of chemotherapy as low as possible.