OBJECTIVES : Most patients diagnosed with mycosis fungoides “MF”, a cutaneous lymphoma, are at early-stage, i.e., ISCL/EORTC cancer stages IA, IB or IIA. Early-stage “ES” disease is usually considered indolent. However, evidence on the epidemiology and differences in survivorship within ES-MF is sparse. Our aim is to describe the differences in survival within ES-MF and to estimate its incidence.

METHODS : Data on all patients diagnosed with MF and recorded in cancer registries comprising the SEER databases (2005 to 2015) were extracted. The patient’s cancer stage data was recorded using the TNM staging system (Tumour, Nodes and Metastasis, 6^th edition). From this the patients were classified with early-stage disease in accordance with ISCL/EORTC staging. Incidence of MF was derived from appropriate denominators provided by SEER for the same period and ES-MF incidence was estimated by applying the published proportion diagnosed at early stage (Talpur 2012: 71%).

RESULTS : The incidence of MF was 0.53/100,000 person-years and thus the incidence of ES-MF was 0.38/100,000 person-years. The median age at diagnosis of the 3132 ES-MF patients was 58 years. They were four years younger than advanced-stage patients at diagnosis, and 57% were male. Five-year survival rates were 87%, 83% and 58% for stages IA, IB and IIA, respectively. Compared to stage IA, age and sex-adjusted hazard ratios were 1.30 (1.01-1.67) and 3.47 (2.29-5.27) for IB and IIA, respectively.

CONCLUSIONS : Incidence of ES-MF was low, and survival was significantly worse for stages IB and IIA compared with IA. This indicates a difference in prognosis among patients with ES-MF. Furthermore, the overall five-year survival rate of stage IA (87%) was significantly lower than previously reported (Agar 2010: 94%). Thus ES-MF is not homogeneous and may not be as indolent a disease as generally thought.