Is the WHO classification suitable for skin lymphoma?

Sir: I write to express my disappointment that the recently published Conference Report, covering the World Health Organization classification of neoplastic diseases of lymphoid tissues, presents conclusions that are suboptimal with regard to their applicability to the skin. Although the classification may live up to its claim to be new and exciting for oncologists and general pathologists, its practical use for dermatologists and dermatopathologists appears limited. These new proposals have been built on the previous `REAL' classification but have failed to rectify those concepts in REAL that are now considered obsolete. For example, angiocentricity is now generally regarded as a histological reaction pattern, that is not indicative of just one type of lymphoma. The European Organization for Research and Treatment of Cancer (EORTC) Classification has been the best attempt, to describe the many idiosyncrasies of primary cutaneous lymphoma. It does, however, present problems in areas such as B-cell lymphoma and also has several omissions. 4, 5 Attempts have been made to apply REAL to the skin, but the greatest hope has been in the anticipated WHO classification. Sadly, as the WHO classification has not come up to expectations, without doubt other bodies, such as the new United Kingdom Skin Lymphoma Group, will have to redress matters. The Conference Report admittedly includes some specific facets of cutaneous lymphoma but it is a struggle to find the information in the published article. Confusingly, important information appears nearly hidden in poorly referenced tables at the end of the article. We are told that marginal zone/MALT lymphoma within the skin is easily recognizable by pathologists as a low-grade lymphoma. I was pleased but surprised to read this, as I have attempted to highlight the extent and importance of this type of cutaneous lymphoma for over a decade. This skin variant, however, was not acknowledged in the REAL classification and appeared in the EORTC classification only as an alternative to the outdated term of immunocytoma. As the EORTC has been reluctant to accept a broader concept of marginal zone lymphoma within the skin, it still appears likely that their entry of follicle centre cell lymphoma incorporates examples of the former. The WHO classification, although not listing primary cutaneous B-cell lymphoma as an entity, paradoxically then states that its distinctive histological and clinical features must be indicated in the text, to avoid potential overtreatment. Similarly, it is strange that cutaneous B-cell lymphoma appears as a variant in a table but not in the main list. With no explanation, we are informed that those using the WHO classification must state the site of involvement in their pathology report. By this, did they mean just `skin' or more specific sites such as leg with its debatable worse prognosis. The WHO conclusions on cutaneous T-cell neoplasia are even more confusing. The discussion on cutaneous anaplastic large cell lymphoma starts well, but then deteriorates quickly. Surprisingly, the widely accepted prognostic value of CD30 positivity receives no explanatory mention. Furthermore, as with B-cell lymphomas, CD30 lymphoproliferative disorders are illogically considered sufficiently distinctive to warrant free-text discussion in an histopathology report but not to appear in the classification. Lymphomatoid papulosis is omitted from the classification on the basis of the stated desire to placate patients and insurers. Furthermore, the CD30 group is omitted overall as clinical criteria must be added to morphological criteria to achieve a diagnosis. This is totally bizarre as the multiparameter recognition of specific entities is the whole basis of the REAL and WHO classifications! The requirement for free-text comments in both cutaneous Band T-cell lymphomas suggests that the WHO has scored an `own goal', with its resistance to include formal clinical grouping in its classification. General pathologists will probably ponder over the undefined term of `borderline lesions'. It is also a debatable concept that pagetoid reticulosis and granulomatous slack skin disease are true variants of mycosis fungoides. The classification, presumably by mistake, omits the nasal-type of natural killer lymphoma which occurs particularly in the skin and it is a tedious search to find lymphomatoid granulomatosis in the list of B-cell disease. Noticeable omissions include small/medium cell pleomorphic cutaneous T-cell lymphoma and also intravascular lymphoma. As it is stated to be a proposed classification, presumably it could still be changed? It would be a pity if the proposed book on the WHO classification does not deal with the skin in a more meaningful way.