20-25% of primary cutaneous lymphomas are of B-cell lineage2. The EORTC 1997 classification of cutaneous B-cell lymphomas recognises three main categories:
Primary cutaneous follicle centre cell lymphoma (PCFCCL). This category covers a spectrum form those which are clearly low-grade cutaneous follicle centre lymphomas to lymphomas composed of large B-cell, which would be considered as DLBCL in the WHO classification. Those occurring on the leg are excepted and placed in a different category. The reason for including large B-cell lymphomas with the PCFCCLs is to avoid unnecessarily aggressive chemotherapy, most localised cases being amenable to radiotherapy. A study comparing primary and secondary cutaneous large B-cell lymphomas has been performed.
Primary Cutaneous Large B-cell Lymphoma, other (i.e., not leg type) includes anaplastic or plasmablastic subtypes and T-cell rich B-cell lymphoma. Primary T-cell rich B-cell lymphoma of the skin has an excellent prognosis3.
Large B-cell lymphoma of the leg. This is predominantly a condition of elderly females. There are confluent sheets of centroblasts and immunoblasts forming lesions on the (lower) leg. This is considered a distinct clinicopathological entity of intermediate prognosis. The t(14;18) translocation is not seen but the cells are bcl-2+: they are bcl-6+ but usually CD10-negative3. The five year survival varies from 100% for a single lesion, to 45% for multiple lesions on one leg and 36% for multiple lesions on both legs3.
Skin is the most common extra-pulmonary site involved in pulmonary lymphomatoid granulomatosis, with lesions that are histologically similar to those seen in the lungs.
References
3 Campo E, Chott A, Kinney MC, et al. Update on extranodal lymphomas. Conclusions of the Workshop held by the EAHP and the SH in Thessaloniki, Greece. Histopathology 2006; 48:481-504 FULL TEXT