What are the main treatment phases for ALL and what's the goal of each?

What are the main treatment phases for acute lymphoblastic leukemia and what’s the goal of each?

ALL is a great example of a very classic cancer treatment phasing. The first phase is what we call induction. The second phase is consolidation, and the third phase is maintenance. There are sometimes regimens that use different names for different components of these phases, but the first phase is probably the most intense with most regimens.

The goal of induction is to induce a remission. That means we want to clear the body of all detectable cancer cells. This is very different from what we would call a cure. Remission is not considered the end of therapy. It just means that we clear off all detectable cancer, with the understanding that there is more cancer that needs to be treated. The goal is to reduce the burden of the disease as low as we possibly can.

There are more nuanced goals incorporated into induction today. It used to be that remission meant a very low number of leukemia cells seen in the bone marrow. Now we have more sophisticated testing that looks for what we call submicroscopic disease — disease we cannot see under the microscope. Using advanced technologies, we can detect minor populations of cancer cells down to one cancer cell out of a million cells evaluated. We call this MRD, or measurable residual disease.

After the induction phase, patients generally undergo another bone marrow biopsy. We check for disease under the microscope and add additional tests to look for very small amounts of disease. This information guides the next steps in treatment and also has prognostic significance.

After induction, we move on to consolidation. The goal of consolidation is to consolidate and deepen the remission, making sure it is more stable and eradicating any measurable residual disease that might still be present. Consolidation generally consists of multiple intensive blocks of treatment.

Many regimens, though not all, include a maintenance phase after consolidation. The purpose of maintenance is to prevent relapse, prolong remission, and maintain the deep remission already achieved. Most relapses occur in the early years after finishing the first two phases, so maintenance is intended to reduce that risk.

In general, we divide the treatment of ALL into these standard components: induction, consolidation, and maintenance. The purpose of induction therapy is to clear away the bulk of the disease and induce a complete remission, meaning less than 5% leukemia under the microscope and recovery of blood counts, including healthy neutrophils and platelets.

Consolidation therapy aims to deepen remission and eliminate measurable residual disease. Maintenance therapy is dedicated to sustaining that remission over time.

All treatment phases include central nervous system prophylaxis, including intrathecal chemotherapy delivered into the spinal fluid. Depending on specific aspects of the disease, a stem cell transplant — also known as allogeneic hematopoietic cell transplantation or bone marrow transplantation — may replace some of these treatment components. For example, a patient may have a shorter period of consolidation if the plan is to proceed to an allogeneic stem cell transplant rather than continue with definitive chemotherapy alone.