As already evidenced with the example of PCMZL [20], the detection of somatic mutations in PCFBCL may nevertheless help to differentiate this indolent lymphoma subtype from reactive, B-cell-rich infiltrates, such as Borrelia-associated B-cell pseudo-lymphoma or CD4+ T-cell lymphoproliferation, and last but not least, from other cutaneous B-cell lymphomas such as PCLBCL or PCMZL. This evidence concerns the gene CD4 and primary cutaneous marginal zone B-cell lymphoma.