Scientists Map Genetic Evolution of CLL to Richter Syndrome

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Richter syndrome is an aggressive lymphoma that develops in up to 1% of patients with chronic lymphocytic leukemia (CLL) and it serves as an example of histologic transformation. While recent advances have transformed the treatment landscape of CLL, Richter syndrome remains associated with poor overall survival and understanding of the genetic factors driving evolution of CLL to Richter syndrome is limited. For the most part, the genomic changes that underlie this metamorphosis and push it forward have been obscure, hindering advances in treatment. In a new study presented by Parry et al at the 2022 ASH Annual Meeting and Exposition (Abstract 633), scientists traced these changes in detail, revealing the genomic differences between CLL and Richter syndrome, the molecular pathways by which Richter syndrome emerges, and the existence of multiple subtypes of the disease.

The findings not only break open what was once a "black box" of molecular change but point the way to an earlier diagnosis of the disease, when treatments may be more effective.

“The treatments for CLL and Richter transformation are very different, so it's critical that doctors be able to determine, as early as possible, when CLL has ‘crossed over’ to become Richter,” said study co–senior author Catherine Wu, MD, of Dana-Farber Cancer Institute, the Broad Institute, and Brigham and Women's Hospital. “The traditional method of diagnosing Richter transformation has a number of shortcomings, which can lead to delays in patients' receiving the appropriate treatment. Our findings in this study hold the promise of an earlier, more definitive diagnosis based on the molecular makeup of the tumor cells.”

One of the biggest obstacles to diagnosing Richter transformation is that patients don’t have either CLL or Richter cells, but a mixture of both. And unlike CLL, which is diagnosed from a blood sample, a formal diagnosis of Richter transformation requires a biopsy. But because a biopsy collects tissue from just one area, it may find CLL cells but miss Richter cells lurking right nearby. As a result, a patient may have classic symptoms of Richter transformation, such as swollen lymph nodes, fever, and night sweats, but the biopsy—which ultimately determines the diagnosis—indicates CLL.

Analysis Details

To understand Richter transformation at the molecular level and track how it evolves from CLL, researchers began with tissue samples gathered from 52 patients over a period of years. Samples collected when the patients had CLL were paired with samples taken when they were diagnosed with Richter transformation. The researchers then performed whole-exome sequencing, reading the protein-coding sections of DNA in the samples. Because the samples likely had a mix of cells, they used computational methods on these sequencing data to estimate the proportion of CLL and Richter cells in each one. Knowing the relative levels of different cell types within the samples, they were able to identify the genetic changes that drive the evolution from CLL to Richter transformation.

The researchers discovered a motley assortment of such changes, including mutations in multiple genes; missing or added copies of other genes; duplication of cell genomes; and chromothripsis, which is defined as a splintering and haphazard reassembly of entire chromosomes.

“We see myriad differences between CLL and Richter transformation at the molecular level, with a much more complex genome in Richter transformation, as well as additional driver events,” remarked study co–senior author Gad Getz, PhD, of the Broad Institute and Massachusetts General Hospital. “In addition, we’ve found that Richter transformation exists in a number of different subtypes.”

Subtypes of Richter Transformation

The subtypes are distinguished by their molecular signatures, the specific pattern of genomic anomalies within their cells. These DNA-level differences suggest that the subtypes arrived by taking different routes in evolving from CLL.

“The formation of multiple subtypes can give us insights into the ‘archaeology’ of the disease: what was the molecular make-up of CLL before it transformed into one subtype or another?” Dr. Wu explained.

Being able to identify different subtypes of Richter transformation can be helpful in the clinic: patients with certain subtypes generally fare better than those with others, although the outlook at the present time is poor for all patients with Richter transformation. Scientists hope that advances can improve those prospects.

Plasma Diagnosis

Once researchers knew the genomic features of Richter transformation, they explored whether the disease could be detected by analyzing DNA in patients’ plasma. They sequenced the DNA in 46 plasma samples from 24 patients with Richter transformation. The samples had been collected over a period of years, beginning within 3 years of a diagnosis of Richter transformation and extending through treatment and relapse. The researchers then sequenced the DNA floating freely within the samples.

“We found that genomic features of Richter transformation were indeed detectable in the plasma,” Dr. Wu stated. “We then asked whether such changes could be detected before patients had been diagnosed with Richter’s based on a biopsy.”

“For some patients, we clearly detected Richter transformation–related DNA alterations in plasma that had been collected 1 to 10 months prior to their Richter transformation diagnosis—a time at which they had been undergoing treatment for what was presumed to be aggressive CLL,” Dr. Wu explained.

The upshot is that it may become possible to diagnose Richter transformation through a simple blood test—potentially earlier than it would show up on a biopsy and at a stage where it may be more treatable.

“The current therapies for Richter transformation are of very limited effectiveness, yet there is hope that patients may benefit from novel, more effective agents. Clinical trials of these agents and of stem cell transplant can explore that promise,” Dr. Wu noted. “By the time Richter transformation is diagnosed, however, patients may be very sick, at which point transplant or other new therapies may not be an option…. [D]etecting it early may make a critical difference.”

Learning the molecular hallmarks of Richter transformation led researchers to one further discovery. In a substantial portion of patients, their Richter cells didn’t share a genetic history with their CLL cells—meaning Richter transformation arose independently, with no connection to the earlier disease.

“Looking ahead to future work, we would like to analyze even larger cohorts of patients [with Richter transformation] to obtain a comprehensive characterization of the genomic and microenvironmental landscape of [Richter transformation]; from this, we can discover new and robust therapeutic targets as well as refined molecular subtypes, getting us closer to applying precision medicine to this disease,” added Dr. Getz.

“Our findings suggest that in many patients, the genomic changes in CLL that lead to Richter transformation occur before patients develop symptoms of lymphoma,” Dr. Wu said. “Being able to trace the transition from CLL to Richter’s at a molecular level impacts not only our understanding of the disease but, potentially, our ability to treat it and improve outcomes for patients.”

Disclosure: The study was supported by the National Institutes of Health/National Cancer Institute, a DDCF Physician-Scientist Fellowship, Dana-Farber Flames FLAIR fellowship, ASCO Conquer Cancer Young Investigator Award, the Broad/IBM Cancer Resistance Research Project, the Fishman Family Fund, Force Hemato, a long-term EMBO fellowship, Deutsche Forschungsgemeinschaft, an NCI Research Specialist Award, and the Melton Family Foundation. For full disclosures of the study authors, visit

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