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EPIDEMIOLOGY
For the past several decades, the incidence of pCBCL had been rising, but now appears to have stabilized. pCBCLs may occur more frequently in specific regions of the world. For example, analysis of data from four academic centers in the US showed that they represented only 4.5% of all the cases of primary cutaneous lymphoma registered in those centers. In contrast, pCBCL represented ~25% of all the cases of primary cutaneous lymphoma in the Dutch and Austrian registries for cutaneous lymphomas.
Regional variations have also been observed with regard to the incidence of specific types of pCBCL. In the two largest series published to date, the relative frequencies of follicle center lymphoma and marginal zone lymphoma varied considerably. Follicle center lymphoma represented 71% of all pCBCLs in the Netherlands, but only 41% in Graz; conversely, marginal zone lymphoproliferative disorder (at that time classified as lymphoma) represented 42% of all cases of pCBCL in Graz, but only 10% in the Netherlands. On the other hand, the relative frequency of the third most common type of pCBCL, the diffuse large B cell lymphoma, leg type, was similar in the two series (~15%), indicating that, in these two series, differences in the relative frequencies were confined to B cell lymphomas characterized by an indolent behavior. This suggests that these variations may be due, at least in part, to a different classification of patients in different centers.
In addition to differences in diagnostic and classification standards, true regional variations in the incidence of special types of pCBCL may be due to the presence of different etiologic factors. For example, the association between pCBCL and infection with specific Borrelia subspecies in endemic areas has been known for many years (see below and Ch. 74). This association may explain, in part, regional differences in the incidence of pCBCLs, but the relatively low percentage of such cases (even in countries with endemic Borrelia infections) suggests that other etiologies are also involved in regional variations.
pCBCL affects adults of both sexes. With the exception of precursor B lymphoblastic lymphoma/leukemia (which only rarely represents an example of true pCBCL), CBCLs are uncommon in children and adolescents.