Background: Rituximab, a chimeric antibody targeted to the human CD20 molecule, is a major component of the R-CHOP protocol used to treat patients with diffuse large B cell lymphoma (DLBCL). It is also a very expensive drug. Though the response rate of R-CHOP is higher than that of CHOP alone, patients may still experience a poor response. One possible mechanism that may mediate the poor response to R-CHOP is poor binding of the drug to the CD20 molecule, perhaps due to mutations or polymorphisms of the CD20 gene that affect its structure. To test this hypothesis and perhaps define a new predictor of R-CHOP response, our pilot study evaluated the CD20 gene sequence from patients exhibiting a poor outcome to R-CHOP.
Methods: Eleven patients with DLBCL who exhibited a recurrence of their disease and/or died within 24 months of R-CHOP treatment were categorized as showing poor progression-free survival (poor outcomes). Paraffin-embedded tissue specimens from the original tumors were evaluated for mutations or polymorphisms of the CD20 gene. Furthermore, sections from these patients and as well as from matched control patients who were categorized as good outcome patients (no progression of their disease within 36 months) were stained with anti-CD20 antibody and compared for CD20 protein expression.
Results: DNA sequence analyses revealed that no mutations were observed in DNA from the coding region of the CD20 gene in any of the initial tumors from 11 patients who showed poor outcomes with R-CHOP therapy. One case showed a synonymous single nucleotide polymorphism in exon 2 (C216T; rs2070770; Ile>>Ile). No significant differences in CD20 expression was observed between good and poor outcome patients with R-CHOP.
Conclusions: Our results do not support association of CD20 mutations in specimens of the initial tumor or structural polymorphisms of the CD20 gene with patients who exhibited poor outcomes to R-CHOP.