Anaplastic Large-cell Lymphoma - Diagnosis

Diagnosis

To make this diagnosis under its present system of classification, the WHO the presence of "hallmark" cells and immunopositivity for CD30.

The classification acknowledges as typical, but does not require, immunopositivity for ALK (anaplastic lymphoma kinase) protein. It specifically excludes primary cutaneous T-cell lymphomas and other specific types of anaplastic lymphoma (particularly those of B-cell lineage) with CD30 positivity.

The hallmark cells are of medium size and feature abundant cytoplasm (which may be clear, amphophilic or eosinophilic), kidney shaped nuclei, and a paranuclear eosinophilic region. Occasional cells may be identified in which the plane of section passes through the nucleus in such a way that it appears to enclose a region of cytoplasm within a ring; such cells are called "doughnut" cells.

By definition, on histological examination, hallmark cells are always present. Where they are not present in large numbers, they are usually located around blood vessels. Morphologic variants include the following types:

• Common (featuring a predominance of hallmark cells)
• Small-cell (featuring smaller cells with the same immunophenotype as the hallmark cells)
• Lymphohistiocytic
• Sarcomatoid
• Signet ring