Clinicopathologic reassessment of non-mycosis fungoides primary cutaneous lymphomas during 17 years

Background New classification systems have recently been proposed for primary cutaneous lymphomas (PCLs). The aim of our study was to evaluate the applicability and significance of the new classification systems to the diagnosis and management of non‐mycosis fungoides (non‐MF) PCL. Methods Immunohistochemical restaining, histological reclassification, and clinical follow‐up of all new non‐MF PCL cases during 17 consecutive years were performed. The histological reclassification was performed according to the Revised European–American Lymphoma (REAL) classification, except for lymphomatoid papulosis (Lyp), which was included as an indolent lymphoma, according to the European Organization for the Research and Treatment of Cancer (EORTC) classification. Results During the period 1983–99, 251 new PCL cases were seen, 213 (85%) of which were MF and Sézary syndrome (eight cases), and 38 (15%) of which were non‐MF. Of the latter, 20 (53%) were B‐cell lymphomas, including eight (40%) follicle center lymphoma, follicular (FCLF), eight (40%) marginal zone lymphoma (MZL), two (10%) diffuse large cell lymphoma, and two (10%) unclassifiable cases. Most or all of the lesions did not stain for CD10, CD43, and bcl‐2 protein, and immunostaining for kappa and lambda immunoglobulin light chain restriction was much more useful diagnostically in MZL. Of the 18 primary non‐MF cutaneous T‐cell lymphomas, 13 (72%) were Lyp, all of which were type A, four (22%) were CD30+ anaplastic large cell lymphoma, and one (6%) was natural killer (NK)/T‐cell lymphoma. Except for the NK/T‐cell lymphoma, all the other non‐MF PCLs had an indolent course. Conclusions A minority of the routinely diagnosed PCLs are non‐MF, equally divided between B‐ and T‐cell lymphomas. The REAL classification is applicable to the majority, although it does not include entities such as Lyp; the clinical correlations are not as obvious because most of the non‐MF PCLs tend to have a relatively indolent course.