The chromosomal band 1q21 is the third most frequent site of rearrangement in non-Hodgkins lymphoma after 14q32 and 18q21.
Five genes mapped to this region (BCL9, MUC1, FCGR2B, MUM2, API2) some have been shown to be deregulated by juxtaposition with the IgH genes.

B-cell non Hodgkin Lymphoma (NHL)

The MUC1 region is rearranged in 6% of tumors with 1q21 cytogenetic aberration.

No clear association with a particular NHL subtype has been reported.

Poor prognosis especially in diffuse large cell lymphoma.
May be associated with tumor progression.

A number of 1q21 abnormalities result in an unbalanced chromosome 1 translocation.

Caryotype often complex.
Usually detected with t(14;18)(q32;q21) and t(8;14)(q24;q32) as a secondary chromosomal abnormalitie.

The translocation links sequences 2.4 kpb 3 of the MUC1 gene on chromosome 1 to the IGH4 switch region on chromosome 14. MUC1 gene is intact. The MUC1 gene is brought into proximity with the C gamma 4 and C alpha 2 loci. Downstream of C alpha 2 is an enhancer element implicated in the activation of MUC1 expression.No fusion protein.

Chromosomal translocation involving class switch recombination when DNA strand breaks are introduced into the switch regions of recombining CH genes. Activation of MUC1 translation and transcription. An important role for MUC1 in tumorigenesis has been demontrated in Muc-1 null mice. MUC1 is associated with delayed progression of the tumor (selective advantage, inhibition of cell adhesion).
In addition to activation of MUC1, haploid loss of chromosome 1 long arm also contributes to oncogenesis in some tumors.