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Psoriasis is thought to be associated with an increased risk of lymphoma. We report here the first case of an aggressive primary cutaneous pleomorphic T-cell lymphoma in a patient with psoriasis. The 36-year-old patient, who had previously been treated successively with methotrexate, ciclosporin and etanercept, presented with rapidly growing nodules on the leg. A biopsy confirmed a stage IVa primary cutaneous pleomorphic T-cell lymphoma. Despite treatment with pegylated liposomal doxorubicin, the disease progressed and the patient died 5 months later. This case of pleomorphic T-cell lymphoma was remarkable in both its extremely rapid onset and the aggressive nature of the disease. The onset of this disease in a patient with psoriasis who had been previously treated with immunosuppressive drugs and a tumour necrosis factor (TNF)-α blocker is of major interest. Only eight cases of cutaneous lymphomas associated with treatment with TNF-α blockers have been published previously. Most of these eight cases related to anti-TNFα antibodies; only two were linked to etanercept.

Making a differential diagnosis between early mycosis fungoides and parapsoriasis is often difficult at the clinical and histological level. The aim of this study was to explore markers that could help in this process. A total of 88 patients were included in 2 categories: large plaque parapsoriasis and digitiform parapsoriasis. A histological examination was performed for each patient, and expression of the antigen My7 (CD13), which is lacking in cutaneous T-lymphomas (but not in inflammatory lesions) and rearrangement of the T-cell receptor gene were analysed. A histological aspect of epidermotropic cutaneous T-cell lymphoma was observed in 23.5% of cases of large plaque parapsoriasis and 15% of cases of digitiform parapsoriasis. A disappearance of My7 antigen was noted in the 2 forms of parapsoriasis, more frequently when there was cutaneous T-cell lymphoma histology. A cutaneous clone was observed in 10.3% of cases of large plaque parapsoriasis, but not of digitiform parapsoriasis. For 3 patients, a cutaneous clone and a disappearance of My7 were associated with a non-specific histology. Considering these histological, immunological and molecular biological data, it appears that My7 antigen combined with T-cell clone may help the dermatologist to confirm the diagnosis of early mycosis fungoides. Moreover, further studies will determine whether CD13 is an early prognostic marker of evolution of a parapsoriasis to mycosis fungoides. Finally, these results demonstrate that digitiform parapsoriasis can be an early stage of MF.