Abdul Mannan/LinkedIn

Mar 10, 2026, 04:15

Abdul Mannan: NK Cell ALL and the Diagnostic Challenge of a Provisional Entity:

Abdul Mannan, Consultant Hematologist at Betsi Cadwaladr University Health Board, shared a post on LinkedIn:

“Most haematologists have never seen NK-Cell ALL.

That’s not surprising. It’s rare. It’s poorly defined. And even the WHO calls it a “provisional entity.”

But if blasts are CD56+ and you can’t fit them neatly into T-ALL, AML, or BPDCN, you need to think about NK-LL.

Here’s what keeps this diagnosis honest:

CD56+ blasts, usually CD34+ and CD7+, with germline TCR configuration

No single marker confirms true NK lineage in every case

Must actively exclude B-cell, myeloid, and plasmacytoid dendritic cell lineage

BPDCN looks similar but is usually CD4+ and CD123+, NK-LL is not

ETP-ALL overlaps heavily, especially if cCD3 is present

Reported mutations include NOTCH1, ETV6, and JAK3

The exam trap?

Diagnosing NK-LL from CD56 alone.

CD56 is expressed in AML, T-ALL, and BPDCN.

It means nothing on its own.

Treatment data is thin.

Most centres use ALL-type induction. Stem cell transplant is often needed.

Relapse is real.

Outcomes are hard to predict because reliable data is limited to small case series.

This remains a diagnosis of exclusion.

Panel-based immunophenotyping and molecular testing are non-negotiable.

Have you encountered a CD56+ acute leukaemia that didn’t fit the usual categories?

How did you work it up?”

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