Peripheral blood tests aid leukemia surveillance for bone marrow failure

For most people, the specter of a life-changing cancer diagnosis is a scary but distant possibility. For those predisposed to developing cancer, such as children with high-risk bone marrow failure syndromes, that possibility looms large, peaking once a year during their annual bone marrow analysis. At that time, they learn if myelodysplastic syndrome (MDS), which lowers blood cell production, or leukemia, emerged since their last bone marrow exam, a test which is arduous for both patients and clinicians. Those prolonged periods between these challenging exams represent a potential gap where a diagnosis could be missed. Clinical researchers from St. Jude have a potential solution in easy and frequent peripheral blood tests. Findings from their work were published recently in Blood.

“We need to be very quick to identify if these bone marrow failure conditions have become pre-leukemic,” said corresponding author Marcin Wlodarski, MD, PhD, Department of Hematology. “We want to detect these myelodysplastic syndrome and leukemia changes as early as possible, because affected children have a much better chance of survival when we transplant them earlier.”

Bone marrow transplantation is used to treat leukemias that occur due to bone marrow failure. However, transplantation can be challenging and risky, so clinicians want to be sure it is truly needed. Bone marrow analysis is the gold standard for detecting these pre-leukemic clones — a small population of blood cells with genetic characteristics that are associated with cancerous transformation. Despite the high quality of the test, it can also be risky, as it requires patients to undergo anesthesia. For this reason, its use is typically restricted to once a year, though some patients require more frequent analyses, and some families refuse it, highlighting the need for an alternative.

All blood cells ultimately originate in the bone marrow, so peripheral blood from a simple blood draw could potentially be used to complement bone marrow analysis. Wlodarski’s team, co-led by Enrico Attardi, MD, PhD, Department of Hematology, and Nathan Gray, PA-C from the Center of Advanced Practice, tested this possibility for pediatric patients, as the approach had shown some merit in adults. However, children develop much smaller clonal populations, so there was some question as to whether the peripheral blood test could be sensitive and specific enough to detect them.

“For the first time in pediatric patients with bone marrow failure, we found that we could detect the same clones in both peripheral blood and bone marrow,” said Gray, who provided clinical care and collected data for the study. “While bone marrow analysis has been the gold standard, our findings show that peripheral blood offers remarkably high sensitivity and specificity for detection.”

Finding the limits of peripheral blood analysis for detecting pre-leukemic clones

While peripheral blood tests performed well, the study also found limitations, based on the type of clone. There are two major categories of pre-leukemic genetic changes: somatic mutations, which comprise small DNA sequence changes, and large chromosomal changes, composed of structural alterations in chromosomes. To find these changes in both bone marrow and peripheral blood, the scientists used two methods, Next Generation Sequencing (NGS) and a Single Nucleotide Polymorphism array (SNP-A), uncovering similarities and differences in what could be uncovered based on the sample’s source.

“For the somatic mutation testing using the NGS gene panel, sensitivity was much higher; we were able to find clones making up 1% of the blood cell population, giving good congruency between bone marrow and peripheral blood tests,” Wlodarski said. “But for chromosomal changes, the method had less sensitivity, requiring a clone to be over 15-20% of the peripheral blood cell population, making it less effective at identifying these changes compared to bone marrow analysis.”

Though peripheral blood had a lower performance when detecting large chromosomal changes, the peripheral blood tests did have one notable advantage. “The specificity is 100%,” Wlodarski continued. “That means, if we find some chromosomal change in peripheral blood, we know for sure this is real, as we always found the same clone present in the bone marrow.”

In the future, finding a large chromosomal change in peripheral blood will trigger an immediate new bone marrow analysis to confirm the observation, which will lead to a faster path to a cure.

Proof is in the peripheral blood test’s performance

During the study, pediatric patients were observed during their standard care and surveillance over the course of five years. That allowed the peripheral blood test to detect pre-leukemic changes as they developed, providing direct evidence of its utility.

“In one case, we saw a child with Shwachman-Diamond syndrome gain a somatic p53 mutation in peripheral blood testing,” Wlodarski explained. Another St. Jude investigator, Alyssa Kennedy, MD, PhD, Department of Hematology, had previously characterized how mutations in the gene for the tumor suppressor p53 can drive leukemia in these patients, requiring the bone marrow failure clinicians to watch the patient more closely, watching the clone double in six months. “That led us to do the bone marrow analysis earlier, so we were able to catch the leukemia very, very early,” Wlodarski said. “The patient then underwent a successful bone marrow transplant and is alive now, over one year later.” This was particularly impressive, as patients with Schwachman-Diamond syndrome who develop full-blown leukemia have a 20-30% survival probability, emphasizing the need to detect the cancer early.

In another case, a patient received multiple inconclusive bone marrow analyses. They showed prolonged and unexplained cytopenia, low blood cell numbers, indicating a problem, but not specifying its exact nature, thus making planning treatment challenging. Peripheral blood testing revealed mutations characteristic of acute myeloid leukemia, prompting further testing and eventual diagnosis.

“We detected chromosomal changes in the peripheral blood,” Wlodarski said. “This triggered additional testing and appropriate therapy for their leukemia, showing how peripheral blood testing can complement bone marrow analysis, or support alternative diagnostic testing when a bone marrow exam is not possible, or results are inconclusive.”

Putting pediatric peripheral blood tests in perspective

Before the study, it was unclear whether peripheral blood testing would effectively detect clones in pediatric patients with bone marrow failure syndromes. With these successful clinical observations, the St. Jude group is proposing a new standard, including peripheral blood tests at regular intervals between bone marrow analyses.

“Many patients won’t develop these pre-leukemic changes, so only some will benefit from earlier detection,” Wlodarski said. “But if we catch leukemia early in those cases, we can give appropriate therapy earlier than we otherwise would be able to and improve outcomes.”

Even with those potential positive outcomes, future implementation faces barriers related to costs and logistics. Still, the St. Jude Bone Marrow Failure program and its affiliates remain committed to figuring out how to implement these solutions for patients predisposed to leukemia.

“This collaboration across departments, especially with our APPs from the Center of Advanced Practice and genetic counselors, was essential to this work,” Wlodarski said. “Peripheral blood testing now gives us a new way to improve surveillance in children with bone marrow failure syndromes and detect these dangerous changes earlier, ultimately saving more children’s lives.”