Malignancies In the placebo-controlled period of the psoriasis clinical studies, the incidence of malignancies excluding non-melanoma skin cancer was 0.25 per 100 patient-years of follow-up for ustekinumab-treated patients (1 patient in 406 patient-years of follow-up) compared with 0.57 for placebo-treated patients (1 patient in 177 patient-years of follow-up).