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Genetic Testing Predicts CLL Prognosis

Laino, Charlene

doi: 10.1097/01.COT.0000287828.01853.f5
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SAN DIEGO—Genetic testing can help predict the prognosis of patients with chronic lymphocytic leukemia (CLL), a trio of studies presented here at the American Society of Hematology Annual Meeting suggests.

One study showed that fluorescence in situ hybridization (FISH) analysis can detect genetic abnormalities in four of five CLL patients, and that the specific abnormality correlates with the response to treatment and survival.

But FISH is not perfect, and other researchers found that testing for chromosomal translocations can pinpoint patients with a poor prognosis that might otherwise be missed.

And a third study showed that high ZAP-70 expression, as measured by flow cytometry, can also be used to identify a subgroup of CLL patients with an unfavorable prognosis that might escape detection on standard testing.

Together, the research “helps explain what we have been seeing in the clinic for years, that CLL is not a homogenous entity,” said session co-moderator Mark A. Weiss, MD, Associate Attending Physician in the Leukemia Service at Memorial Sloan-Kettering Cancer Center.

“The reason that some people have slow-moving disease and can go years without treatment while others have a very aggressive course has to do with what is going on at the level of DNA. If you have certain chromosomal abnormalities, you'll do worse, while others have a more benign course.”

FISH-ing for Prognosis

In the first study, Daniel Catovsky, MD, a hematologist/oncologist with the Royal Marsden National Health Service Foundation Trust in London, reported that CLL patients who are found to have 17p deletions on FISH have the worse prognosis, while those with 13q deletions or who have no deletions fare the best.

What was really surprising, he said, is that “for the patients whose proportion of 17p deletion lymphocytes exceeds 20%, two-year survival is only 34%—as bad as acute leukemia.”

The researchers studied 373 CLL patients randomized to receive chlorambucil, fludarabine alone, or fludarabine plus cyclophosphamide.

FISH analysis using five probes showed that 80% of patients had genetic abnormalities, with 11% having a 17p deletion, he said. Also, 60% had a 13q deletion, 15% had trisomy 12, 8% had a 6q deletion, and 19% had an 11q deletion. Some had more than one abnormality.

Regardless of treatment, the specific abnormality correlated with response, Dr. Catovsky said. Forty-four percent of the patients with a 17p deletion either progressed or did not respond, compared with 14% of those with 13q deletions, and 24% of those with 11q deletions.

The two-year survival rate in patients with 13q deletions was 96%, compared with 87% for those with no deletions, and 67% for those with 17p deletions.

Schering Health Care helped support the work.

17p Deletions Predict Poor Response

Since almost half of the patients with the 17p deletion are primary nonresponders or show progressive disease following first-line therapy, the researchers wanted to find out why some of these patients responded and others did not, Dr. Catovsky said.

“What became apparent was that the higher the percentage of 17p deleted cells, the greater the proportion of nonresponders.”

Using 20% as a cutoff, they found that 17% of the patients with less than 5% deletion were nonresponders, compared with 79% of the patients with more than 20% deletions. The 17% of patients who fell in the middle also did not respond, he added.

The next step, Dr. Catovsky said, is to find out whether targeted therapies can overcome the low response rates with patients with genetic abnormalities that carry a poor prognosis.

The session's other co-moderator, Michael Kneba, MD, Director of the Department of Hematology at the University of Kiel in Germany, said the research is noteworthy in that it is one of the first prospective studies to confirm that chromosomal aberrations are a very strong prognostic factor in CLL.

Translocations Linked to Poor Prognosis

In the second study, Christine Mayr, MD, a medical oncologist at Medical Clinic III at Ludwig-Maximilians-University in Munich, reported that a new karyotyping technique, CD40-ligand-enhanced cytogenetics (CEC), is able to detect chromosomal aberrations in CLL, including some that are undetectable by FISH or conventional metaphase cytogenetics.

More importantly, patients who have these translocations, regardless of the specific abnormality, have a poor prognosis, she said.

The work builds on the team's previous research that showed that stimulation of CLL cells with CD40 ligand can induce cell-cycle progression and increase the frequency of metaphases of CLL cells, which are then suitable for chromosome banding, she said.

For the study, the researchers obtained blood samples from 95 CLL patients and performed both FISH and CEC analysis on all of them.

Eighty percent showed abnormalities on FISH, while CEC detected abnormalities in 90% of the samples, Dr. Mayr reported. “There was involvement of every chromosome other than X,” she added. Half of the patients had two or more aberrations, she said, with up to 14 found in some patients.

Mark A. Weiss, MD: “The studies help explain what we have been seeing in the clinic for years—that CLL is not a homogenous entity.”

One Third of Patients Affected

The most interesting finding, according to Dr. Mayr, was that 35% of all CLL patients had translocations, half of which were balanced and half of which were unbalanced. And all these patients had a poor prognosis.

Among the findings:

  • Treatment-free survival was significantly longer in patients with no translocations: 106 vs 28 months for those with translocations.
  • One fourth of patients with 13q deletions as a single aberration on FISH analysis also showed translocations by CEC. These patients had a significantly shorter treatment-free survival: 36 months, compared with 132 months for patients with a 13q deletion but no translocations.
  • All patients with 17p deletions showed translocations and had a poor prognosis.

Overall survival rates were also significantly lower in those with translocations than in those with no translocations, with unbalanced translocations driving most of the difference, Dr. Mayr said.

A multivariate analysis that included Binet stage, the presence of three or more chromosomal aberrations, CD38 expression, and 11q and 17p deletions confirmed that the occurrence of translocations had the greatest impact on treatment-free survival, she said.

Dr. Weiss said that in his view, this was an extremely important and novel study. “The fact that these recently recognized translocations carry a poor prognosis is real news,” he said.

“With FISH, you can't test for everything; you are limited by what specific probes are used. But with karyotypic analysis you can look at the whole genome and might see abnormalities that are missed using a standard set of FISH probes.”

ZAP-70 Expression Predicts Progression

In the third study, Francesc Bosch, MD, Senior Specialist in the Department of Hematology at Hospital Clinic in Barcelona, Spain, reported that both time to progression and overall survival are significantly affected by ZAP-70 status.

The aim of the study was to analyze the distribution of different prognostic parameters according to ZAP-70 expression in 260 patients with CLL, she said. ZAP-70 was determined by flow cytometry, with high expression being defined as more than 20% ZAP-70-positive CLL cells.

The median age of the patients, about three fifths of whom were male, was 62. Thirty percent of patients were considered to have high expression of ZAP-70 using the predefined criteria, Dr. Bosch reported.

The study showed that the median time to progression was 2.5 years in those with high ZAP-70 expression, compared with 9.9 years in those with lower expression. However there was no correlation with response to therapy, with 39% of those with low expression and 40% of those with high expression responding.

But the median overall survival time was significantly affected by ZAP-70 status: 8.5 years for those with high expression vs 16.3 years for those with lower expression, she said.

Among the parameters that were significantly associated with a high ZAP-70 expression were lymphocyte doubling time of more than 12 months, atypical morphology, bone marrow infiltration of greater than 60%, greater than 20% CD38 expression, and development of Richer syndrome, Dr. Bosch said.

Dr. Kneba noted that gene array studies have shown that ZAP-70 is overexpressed in CLL cases.

“The new study confirms that it is an important marker, with implications for prognosis,” he said.

Importantly, flow cytometry for ZAP-70 expression can be done in about a day, he noted, while DNA sequencing takes at least a week and is much more costly.

© 2005 Lippincott Williams & Wilkins, Inc.
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