Tam et al correlated the response of a patient with chronic lymphocytic leukemia (CLL) to rituximab based on the FISH subtype. This can help to identify a patient who may or may not respond to this form of therapy. The authors are from the University of Texas M.D. Anderson Cancer Center in Houston.
The response to rituximab (humanized monoclonal antibody to CD-20) correlates with the number of CD20 sites on the lymphocyte surface.
FISH Subtype
Median Number of CD20 Sites per Cell
Partial Response or Better to Rituximab
trisomy 12 (+12)
23,600
93%
13q deletion
10,800
73%
17p deletion
9,300
73%
negative
8,800
73%
11q deletion
5,900
50%
where:
• Most patients show a single subtype. A few patients may show 2.
• Measuring the number of CD20 sites per lymphocytes might be helpful if the test is available. Responders had a median number of 8,700 sites per cell while nonresponders had a median number of 6,400. This might most helpful for a patient with 11q deletion since some patients had a high number of sites.
• Rituximab therapy could select for clones of cells with poor CD20 expression.
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