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We have read with interest the editorial by De Wolf-Peeters and Achten, which recently appeared in your journal.1 As the authors state in this editorial, the lymphoma entity designated anaplastic large cell lymphoma (ALCL) is probably more heterogeneous than currently recognised in the REAL/WHO classification.
Recent studies have shown the existence of a true clinicopathological entity among the CD30 positive anaplastic lymphomas; namely, an ALCL subtype characterised by a specific chromosomal aberration, involving the anaplastic lymphoma kinase (ALK) gene on 2p23, and by excellent prognosis.2, 3 ALK expression is found in 30–60% (depending on the age of the population studied) of systemic ALCLs with (primary) nodal involvement. It is not found in primary cutaneous and other extranodal ALCLs.4, 5
The remaining controversy concerns ALK negative systemic nodal ALCL, which may be morphologically indistinguishable from primary cutaneous ALCL, but which runs an aggressive clinical course compared with primary cutaneous ALCL. Furthermore, the distinction between ALK negative systemic ALCL and peripheral T cell lymphoma, not otherwise specified (T-NOS) is drawn into question because the formerly acknowledged difference in prognosis between ALCL and peripheral T-NOS might result from the favourable prognosis of ALK positive ALCL. Thus, as the authors correctly state, criteria for proper distinction between (ALK negative) systemic ALCL and extranodal ALCL, as well as peripheral T-NOS, are needed to determine therapeutic strategies.
Recently, we identified a biological prognostic marker for ALK negative systemic ALCL.2 We found that a high percentage (≥ 15%) of activated cytotoxic T lymphocytes (CTLs), present in the reactive infiltrate, is related to poor overall and progression free survival. This biological prognostic marker remained independent of, and seemed more sensitive than, established clinical parameters (such as the international prognostic index) in determining clinical outcome. The same relation between high numbers of activated CTLs and poor prognosis was found by our group for Hodgkin's disease.6 These studies suggest that the interaction between tumour cells and reactive immune competent lymphocytes might be more important to clinical outcome than the morphology and immunophenotype of the lymphoma cells. As such, studies intending to clarify the distinction between the above mentioned lymphoma subtypes, and to provide prognostic markers, should take into account immunobiological properties as well as clinical and histological features.