Angioimmunoblastic T-cell lymphoma with a clonal plasma cell proliferation that underwent immunoglobulin isotype switch in the skin, coinciding with cutaneous disease progression.

Plasma cell proliferations in specific cutaneous lesions of angioimmunoblastic T-cell lymphoma(AITL) are very uncommon. Here, we report a case of clonal plasma cell proliferation in skin with heavy-chain-immunoglobulin-isotype-switch after cutaneous disease progression. Histopathologically, initial plaque lesions were suggestive of marginal-zone B-cell-lymphoma. Nevertheless, this 77-year-old lady was diagnosed with AITL after the progression of skin lesions from plaques to nodular tumors. A lymph node biopsy confirmed the diagnosis. Both cutaneous specimens showed a polymorphic cellular infiltrate with atypical T-cell-lymphocytes arranged in a pseudonodular pattern that expressed CD3, PD1 and BCL6, with patchy expression of CD30. Interestingly, a slight IgG-Lambda plasma cell component was seen at the periphery of the infiltrate in the first specimen which increased in number in the later nodular lesion, showing not only Lambda light chain restriction and IgG but also IgG4. PCR studies for IgH and TCR genes showed an IgH clonal peak on both skin lesions but not on lymph node biopsy. On the contrary, the same clonal TCR peak was found in the three specimens. Neoplastic follicular helper T-cells within cutaneous-specific microenvironment could be responsible for the modulation of the immunoglobulin isotype class switch change. Further studies are needed to support this hypothesis.