WHO soft tissue and bone tumours, 6th edition: 19 new entities, and 'pattern' replaces 'variant'

The 2026 WHO Classification of Tumours of Soft Tissue and Bone, summarised in the American Journal of Surgical Pathology by its editors, covers 116 soft tissue tumours, 46 bone tumours, 18 vascular tumours, four undifferentiated spindle and round cell sarcomas, six haematopoietic and dendritic cell neoplasms and six genetic syndromes — 62 sarcomas in all.

Nineteen new tumour types were added. The edition sharpens its definitions: a tumour type differs from others in several dimensions; a subtype differs in at least one, ideally with different treatment or outcome; and a morphological pattern, which replaces the term 'variant', matters for recognition but not for behaviour. Essential and desirable diagnostic criteria have been refined with different resource settings in mind.

That last change matters in Indian practice, where molecular confirmation is not always available. Reports should state which essential criteria were met and whether a desirable molecular test was done or is pending.

• Update soft tissue and bone reporting templates to the 6th edition terminology.
• Use 'morphological pattern' rather than 'variant' where the distinction has no prognostic meaning.
• State in the report which essential criteria were met, and whether desirable molecular tests were done.
• Review the 19 new entities before signing out unusual spindle cell or round cell tumours.
• Flag cases where a diagnosis rests on criteria that need molecular confirmation not available locally.

Why it matters

The classification is the shared language oncologists and surgeons act on, and the resource-setting criteria make it workable where molecular testing is limited.

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