Due to lack of a defined common pathogenic mechanism or specific clinicopathological features (other than primary cutaneous anaplastic large-cell lymphoma), haematopathologists have debated whether the diagnostic criteria for ALK– anaplastic large-cell lymphoma define a specific entity or if ALK– anaplastic large-cell lymphoma should be included in peripheral T-cell lymphoma unspecified. The gene discussed is ALK; the disease is anaplastic large cell lymphoma.