Classification of primary cutaneous large cell lymphomas.

Primary cutaneous large cell lymphomas represent a heterogeneous group of malignant lymphomas of T- and B-cell origin. Recent studies have been successful in delineating some well-defined clinicopathologic entities within this group. Primary cutaneous follicular (germinal) center cell lymphomas are the most common type of CBCL. These lymphomas generally present with localized skin lesions on the trunk or scalp. They have an indolent clinical course, are highly sensitive to radiotherapy, and have a favorable prognosis. Within the group of primary cutaneous T-LCL, distinction primarily should be made between CD30-positive (> 75% or large clusters of tumor cells) and CD30-negative (no or few scattered positive cells) T-LCL. Primary cutaneous CD30-positive T-LCL, which includes both anaplastic and non-anaplastic subtypes, have recently been defined as a distinct clinicopathologic entity with a favorable prognosis. The overlapping clinical and histological features with LyP suggest that both conditions are part of a broader spectrum of primary cutaneous CD30-positive lymphoproliferative disorders. Primary CD30-negative T-LCL generally are associated with a poor prognosis (4-year-survival, < 25%). Reports on this group are still few, however, and further studies are required to define subgroups with a more favorable prognosis within this heterogeneous group of lymphomas.