Recently, Hernandez et al1 reported an interesting case of progression of undiagnosed T-cell lymphoma during efalizumab therapy in a 32-year-old man with a 2-year history of a pruritic, erythematous dermatitis that was erroneously diagnosed as psoriasis. The patient developed skin tumors within 3 months of stopping a 4-month cycle of efalizumab therapy, and a diagnosis of tumor-stage erythrodermic mycosis fungoides (MF) was made. A retrospective review of skin biopsy specimens taken before efalizumab therapy had begun confirmed histologic features consistent with pilar MF. The authors conclude that the timing of the tumor-stage progression and initiation of efalizumab treatment in their patient, although not direct evidence of causation, raises suspicion, and they suggest efalizumab avoidance, or at least extreme caution in its use, for patients with a history of lymphoma. In fact, the drug label warns that caution should be used if the drug is being considered for patients at high risk for or with a history of malignant neoplasm.