Introduction: Who Should Be Tested and When

If you have been diagnosed with acute myeloid leukemia, which is a type of blood cancer, your doctor will likely recommend testing for something called FLT3 mutations. This test is important for anyone who receives an AML diagnosis because it helps determine the best treatment approach for your specific case.^[1]

Testing for FLT3 mutations should happen as soon as possible after an AML diagnosis is made. According to medical guidelines, it is particularly important to test for FLT3 in patients who have what doctors call “normal cytogenetic laboratory findings,” meaning their chromosomes look normal under standard testing. The identification of FLT3 mutations has important implications for how your disease will be managed and what kind of treatment you might receive.^[1]

Doctors recommend getting test results quickly, ideally within 48 to 72 hours, especially for patients who are eligible for intensive induction chemotherapy. This fast turnaround is crucial because it allows the medical team to start appropriate treatment without delay. The presence or absence of a FLT3 mutation can significantly influence treatment decisions right from the start.^[3]

Understanding FLT3 and Its Role in AML

The FLT3 receptor is a protein that sits on the surface of certain blood cells. It belongs to a family called tyrosine kinases, which are proteins that help control cell growth and division. In healthy bone marrow, FLT3 is found on special stem cells marked with something called CD34, as well as on immature blood-forming cells. These cells are found not only in bone marrow but also in other blood-forming organs like the spleen and liver.^[3]

When FLT3 mutations occur, they change how this protein works. The mutations are quite common in people with AML. About 25 to 30 percent of adults newly diagnosed with AML have what is called an internal tandem duplication, or FLT3-ITD for short. Another 5 to 10 percent have a different type of mutation called a tyrosine kinase domain mutation, abbreviated as FLT3-TKD.^[5][8]

These mutations can occur alongside other genetic changes in the cancer cells. For example, FLT3 mutations are sometimes found together with NPM1 mutations, which are generally considered a favorable sign, or with CEBPA mutations and various chromosomal abnormalities. Understanding the full genetic picture helps doctors predict how the disease might progress and respond to treatment.^[3]

Classic Diagnostic Methods

Blood and Bone Marrow Testing

The primary way to detect FLT3 mutations is through laboratory analysis of blood or bone marrow samples. These samples contain the cancer cells that doctors need to examine for genetic changes. The testing process involves extracting genetic material from these cells and looking specifically for alterations in the FLT3 gene.

The test looks for two main types of FLT3 mutations. The more common type is the FLT3-ITD mutation, where a section of the gene gets duplicated and inserted back into itself. This happens in roughly 25 to 30 percent of people with AML. The less common type is the FLT3-TKD mutation, which involves specific changes in the part of the gene that codes for the tyrosine kinase domain. This type occurs in about 6 to 10 percent of AML cases.^[3][8]

In rare situations, a patient might have both an ITD mutation and a TKD mutation at the same time. When both types are present together, it typically means worse clinical outcomes compared to having just one type of mutation. This is why precise identification of the mutation type is so important for predicting how the disease might behave.^[3]

Understanding Test Results and Prognosis

The FLT3-ITD mutation carries particular significance when it comes to predicting outcomes. While having this mutation does not affect a patient’s ability to achieve what doctors call “complete remission” with initial treatment, it does have other important effects. People with FLT3-ITD are at higher risk for the disease coming back after treatment, have decreased disease-free survival, and generally have shorter overall survival compared to those without the mutation.^[3]

The FLT3-TKD mutation, on the other hand, does not seem to have a known effect on prognosis. This means that patients with this type of mutation may have outcomes similar to those without any FLT3 mutation, though research in this area continues to evolve.^[3]

Research has shown that patients with high levels of a protein called CHK1, which is often elevated in FLT3-ITD positive AML, tend to have lower overall survival rates and disease-free survival rates compared to those with low CHK1 levels. This additional biomarker provides extra information about prognosis beyond just knowing the FLT3 mutation status.^[4]

Additional Molecular Testing

Beyond testing specifically for FLT3 mutations, doctors often perform other genetic and molecular tests as part of a complete diagnostic workup. These additional tests help build a comprehensive picture of the disease. Standard AML diagnostics typically include examination of chromosomes to look for structural abnormalities, testing for other common gene mutations like NPM1 and CEBPA, and various blood counts and chemistry panels.

All of these tests together help doctors classify the AML into risk categories. FLT3 mutations are considered independent poor prognostic factors, meaning they suggest a more aggressive disease course regardless of other features. However, the complete genetic and molecular profile is always considered when making treatment decisions.^[3]

Diagnostics for Clinical Trial Enrollment

When researchers design clinical trials to test new treatments for FLT3-positive AML, they establish specific criteria that patients must meet to participate. These criteria almost always include confirmation of the FLT3 mutation through laboratory testing. The mutation status is typically verified using standardized molecular diagnostic methods before a patient can enroll.

Different clinical trials may have different requirements regarding which type of FLT3 mutation is acceptable. Some trials focus specifically on FLT3-ITD positive patients, while others may accept patients with either ITD or TKD mutations. This is because different investigational drugs may work better against one type of mutation versus another.^[5]

For example, the landmark RATIFY trial, which led to the approval of the drug midostaurin for FLT3-positive AML, enrolled patients who had either FLT3-ITD or FLT3-TKD mutations. The trial included 717 patients between ages 18 and 59 with newly diagnosed AML who tested positive for FLT3 mutations. All participants had their mutation status confirmed before being randomly assigned to receive either midostaurin or placebo in combination with standard chemotherapy.^[3][5]

Other trials, such as those testing second-generation FLT3 inhibitors like quizartinib, crenolanib, and gilteritinib, also require documented FLT3 mutation status as an entry criterion. These newer drugs are designed to be more selective and potent against FLT3, so confirming the presence of the mutation is essential for determining whether a patient might benefit from the experimental treatment.^[3]

Beyond just confirming the mutation, clinical trials may also require additional baseline testing. This can include measurements of how well major organs like the heart, liver, and kidneys are functioning, complete blood counts, bone marrow examinations to assess the percentage of leukemia cells, and sometimes imaging studies. These baseline tests help ensure that patients are healthy enough to participate safely in the trial and provide reference points for measuring how well the treatment works.^[5]

Monitoring During and After Treatment

Once treatment begins, whether as part of a clinical trial or standard care, ongoing monitoring is essential. Doctors will periodically retest bone marrow and blood samples to see how the leukemia cells are responding to therapy. These follow-up tests may again include FLT3 mutation testing, as sometimes the genetic profile of the disease can change over time, particularly if the disease returns after initial treatment.

Some patients who initially respond to FLT3 inhibitor drugs eventually develop resistance, meaning the treatment stops working. When this happens, repeat genetic testing may reveal new mutations that explain the resistance. Identifying these additional changes can sometimes guide decisions about switching to different treatments or trying combination approaches.^[5]

The frequency and type of monitoring tests vary depending on the treatment regimen and the patient’s response. Regular blood counts, bone marrow biopsies, and molecular testing help doctors assess whether the treatment is controlling the disease, whether it needs to be adjusted, or whether the disease is progressing despite therapy.