Prognostic factors and prediction of prognosis by the CTCL Severity Index in mycosis fungoides and Sézary syndrome

Summary Background Cutaneous T‐cell lymphoma (CTCL) is a slowly progressive malignancy for which there is no cure. Therefore, accurate prediction of prognosis is important for the conduct of clinical trials and for counselling of individuals. Objectives To improve prediction of survival in patients with CTCL. Methods Prognostic factors including tumour–node–metastasis (TNM) criteria and the CTCL Severity Index (CTCL‐SI) were analysed using a Weibull model for multivariate analysis in a sample of 62 patients with classical CTCL (mycosis fungoides and Sézary syndrome). The Brier score was used to quantify the quality of individual prediction. Results Estimated 5‐year survival rate (SR5) differed according to TNM stage: stage IA, 100% (95% confidence interval 70–100%); IB–III, 86% (73–100%); IVA, 54% (32–91%); IVB, 0% (0–52%). In a multivariate analysis, two independent prognostic factors were identified: lymph node (P = 0·036) and blood involvement (P = 0·015). A probability of survival model showed correlation of CTCL‐SI with survival in patients with CTCL‐SI > 20 according to the following formula: SR5 = 124–2 × (CTCL‐SI)%. Calibration of SR5 against CTCL‐SI‐independent CTCL subsets revealed underestimation of Sézary syndrome. When CTCL‐SI parameters were adjusted accordingly, the probability of survival model did not change significantly, while SR5 values became adequate. In addition, CTCL‐SI was shown to be superior to TNM by 30% regarding individual predictive power. Conclusions Probability of survival in CTCL can be accurately predicted by a CTCL‐SI‐based survival rate formula. Careful monitoring of lymph node and blood compartments and quantification by CTCL‐SI are reliable tools for follow‐up of patients with CTCL and allow progression‐adjusted prediction of prognosis.