In advice that I have been giving over the past 5 years I have been stressing that CD20 is brighter in patients who have trisomy 12. Indeed we noticed some time ago that trisomy 12 CLL was rather different from other types of CLL . Today, published in the British journal of Haematology comes mathematical confirmation of our observation, from Michael Keating's group .
In patients with trisomy 12 there were 23,603 CD20 antigenic sites per cell compared with 10,781 for del 13q, 9,341 for del 17p, 8,828 for those with negative FISH and 5,886 for those with del 11q. The figures for trisomy 12 and del 11q patients were statistically significantly different.
Does this matter? Yes, because rituximab targets CD20. In the same paper the MDACC group report that the combination of rituximab and GM-CSF produced responses in93% of patients with trisomy 12, 73% in patients with negative FISH, del 13q or del 17p, and 50% in patients with del 11q.
1] Trisomy 12 defines a group of CLL with atypical morphology: correlation between cytogenetic, clinical and laboratory features in 544 patients. Matutes E, Oscier D, Garcia-Marco-J, Ellis J, Copplestone A, Gillingham R, Hamblin T, Lens D, Swansbury GJ, Catovsky D. Brit J Haem 1996 92: 382-8
2] Chronic lymphocytic leukaemia CD20 expression is dependent on the genetic subtype: a study of quantitative flow cytometry and fluorescent in situ hybridization in 510 patients. Tam CS, Otero-Palacios J, Abruzzi LV et al. Brit J Haem 2008 141: 36-40.