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Specific immune therapy‐related cutaneous B‐cell pseudolymphoma with following dissemination

We report two cases of cutaneous B‐cell pseudolymphoma (PCBCL) induced by intradermal antigen injections for specific immune therapy (SIT). In both cases, the lesions had first developed on the area of injection; years later, new lesions appeared far from the original site. The histological, immunohistochemical, and molecular findings of the lesions showed features consistent with the diagnosis of PCBCL in both cases. In particular, the staining for sIg light chains showed a polyclonal pattern, and the molecular analysis by reverse transcriptase‐polymerase chain reaction (RT‐PCR) and Southern blot showed a germ‐line configuration of the Ig heavy chain genes. While the development of PCBCL related to a specific stimulus is well known and widely reported, the development of histologically and immunohistologically identical lesions far from the injection site is definitely worthy of note. This behaviour might be due to the presence of retained antigens in the injection site. This chronic antigenic stimulation could induce the progressive selection – and subsequent dissemination – of antigen‐specific B cell clones.