Risk of mycosis fungoides in psoriatic patients: a critical review.

Psoriasis has been controversially associated with risk of non-Hodgkin lymphoma (NHL) and mycosis fungoides (MF). Also patients who developed MF after systemic treatment for psoriasis have been reported, and some authors suggested that the association between MF and psoriasis is not infrequent. We performed an extensive literature review in order to examine the risk of developing MF in psoriatic patients with a systematic search of the English-language databases. An increased risk for lymphoma overall in psoriatic patients has been found only by three out of seven studies. The risk of developing MF in psoriatic patients has been investigated by different studies in different populations and with different methodologies presenting bias and limitations, and it seems reasonable that misclassification between psoriasis and MF may explain the association reported. In contrast to the large number of psoriatic patients treated with biologicals, only 27 case reports of MF after biological therapy for psoriasis have been reported, and in 10 cases, the initial psoriasis diagnoses were then revised as MF. A true association between MF and psoriasis is possible, but the real incidence and prevalence are still unknown. The reported higher risk of developing MF in psoriatic patients should be reconsidered in the light of the bias of misclassification and the low magnitude reported in previous studies. There is not enough evidence to support a causal relation among biological therapies and MF in psoriatic patients.