Cancer Dictionary · Blood and lymphatic

T-Cell Lymphoma

T-cell and NK-cell lymphomas comprise many distinct entities that behave very differently, from indolent skin-limited disease to rapidly progressive systemic lymphoma. Diagnosis is genuinely hard, expert review changes it in a meaningful proportion of cases, and treatment approaches are less standardised than for B-cell lymphoma. Trial participation is a more prominent part of the discussion as a result.

Also called Peripheral T-cell lymphoma, PTCL, Cutaneous T-cell lymphoma, Anaplastic large cell lymphoma.

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The governing idea

T-cell lymphomas are a diverse group of individually rare diseases where getting the exact entity right is difficult and consequential, and where expert haematopathology changes the diagnosis often enough to be worth arranging routinely.

Before any molecular question

How it usually presents

Usually established first: the specific entity from an adequate biopsy with immunophenotyping, the stage, and whether disease is systemic or skin-limited. Because these diagnoses are individually rare, review at a centre that sees them regularly is routinely recommended.

Usually already established

The specific entity, ideally after expert haematopathology review
Immunophenotype and clonality
Stage, and whether disease is systemic or skin-limited
ALK status where anaplastic large cell lymphoma is diagnosed

Major disease categories

The divisions below are not labels. Each one changes what the treatment discussion is actually about.

Peripheral T-cell lymphoma, not otherwise specified

A diagnosis of exclusion, reached when a case does not fit a defined entity. The label itself signals that the classification is uncertain.

Angioimmunoblastic T-cell lymphoma

A distinct entity with characteristic mutations in epigenetic regulators, often presenting with immune features that can mimic non-malignant conditions.

Anaplastic large cell lymphoma

Divided by ALK status, which carries substantial prognostic weight. A breast-implant-associated form is separately recognised.

Cutaneous T-cell lymphoma

Including mycosis fungoides. Frequently indolent and skin-limited for years, managed on an entirely different pathway from systemic disease.

NK/T-cell lymphoma, nasal type

Strongly Epstein-Barr virus associated, more common in Asian and Latin American populations, with its own distinct treatment approach.

Adult T-cell leukaemia/lymphoma

Associated with HTLV-1 infection, with a defined geographic distribution.

What is discussed

Molecular considerations

The commonly altered genes cluster in epigenetic regulation: TET2, DNMT3A and IDH2, particularly in angioimmunoblastic disease, alongside RHOA G17V which is characteristic of it. ALK rearrangement defines a favourable subgroup of anaplastic large cell lymphoma, and DUSP22 and TP63 rearrangements carry prognostic weight in the ALK-negative group. JAK and STAT pathway alterations occur across several entities. CD30 expression is therapeutically relevant and is assessed across the group. Epstein-Barr virus is central to NK/T-cell lymphoma.

Biomarkers commonly discussed

ALK

Rearrangement defines a favourable subgroup of anaplastic large cell lymphoma.

CD30

Expression is therapeutically relevant across several entities, not only in anaplastic disease.

TET2, DNMT3A, IDH2

Epigenetic regulators, characteristic of angioimmunoblastic disease.

RHOA G17V

Characteristic of angioimmunoblastic T-cell lymphoma.

DUSP22 and TP63

Rearrangements carrying prognostic weight in ALK-negative anaplastic large cell lymphoma.

EBV

Central to NK/T-cell lymphoma, nasal type.

T-cell clonality

Used to confirm that a T-cell population is malignant rather than reactive.

This is not an exhaustive list, and which markers are relevant depends on the individual case. Not every marker listed is assessed in every patient.

What is tested, and from what

Testing, inherited risk and blood-based monitoring

Genomic testing considerations

An adequate biopsy with full immunophenotyping and T-cell clonality assessment is the foundation. Expert haematopathology review matters more here than in almost any other lymphoma, because these entities are hard to distinguish and the distinction changes management. ALK status is established where anaplastic large cell lymphoma is diagnosed. Comprehensive sequencing is used more than in B-cell lymphoma, partly because the standard options are fewer and trial access matters more.

Germline considerations

Most cases are sporadic. Inherited immunodeficiency syndromes predispose to T-cell lymphoproliferative disease, and a background of recurrent infection or autoimmunity in a young patient is a reasonable prompt. Adult T-cell leukaemia/lymphoma is associated with HTLV-1, which is transmissible rather than inherited, and that distinction matters for family members.

Cancer genetics and hereditary risk

ctDNA and liquid biopsy considerations

Circulating EBV DNA is used in NK/T-cell lymphoma, where it is genuinely informative. Broader ctDNA application across T-cell lymphomas is at an earlier research stage than in B-cell disease.

When molecular information matters

Testing that arrives after the decision it was meant to inform has already been made is a common and avoidable problem. This is the sequence in which molecular information tends to become relevant.

At biopsyAn adequate sample with full immunophenotyping. This is where most diagnostic difficulty in this group originates.
Before treatment planningExpert haematopathology review is worth arranging, because it changes the diagnosis in a meaningful proportion of cases and everything follows from it.
At diagnosisALK status where anaplastic large cell lymphoma is diagnosed, and CD30 expression across the group.
Early in the discussionTrial options, because standard options are fewer here than in B-cell lymphoma and eligibility narrows with each line.
At relapseRebiopsy and reassessment, particularly of CD30 expression.

Take these to your team

Questions worth raising

When a decision is being made

Questions worth raising with a treating team.

Has the exact entity been established, and has expert haematopathology review been arranged?
Has T-cell clonality been assessed to confirm the population is malignant rather than reactive?
In anaplastic large cell lymphoma, has ALK status been established?
Has CD30 expression been assessed, since it is therapeutically relevant across several entities?
Have trial options been reviewed early, given how few standard options exist for many of these entities?

At progression, recurrence or resistance

The molecular picture at diagnosis is not always the molecular picture later.

Has the original diagnosis been revisited, given how often these entities are reclassified on review?
Has CD30 expression been reassessed at relapse?
Have referral to a centre that sees these diseases regularly and trial options both been considered?

What shapes eligibility

Clinical trial considerations

Trials matter more in T-cell lymphoma than in most lymphomas, because standard options are fewer and less well established. Eligibility is written by precise entity, so an imprecise diagnosis is a practical barrier to access as well as to treatment.

Ask about trial matching

Plain-language glossary for this entry (5 terms)

Term	What it means
Immunophenotype	The pattern of markers on the cell surface, used to establish what kind of cell a lymphoma came from.
Clonality	Whether a population of T-cells descends from one ancestor, which distinguishes malignant from reactive.
Not otherwise specified	A label meaning the case did not fit any defined entity. It signals uncertainty rather than a diagnosis.
Mycosis fungoides	The most common cutaneous T-cell lymphoma. Often indolent and skin-limited for many years.
HTLV-1	A virus associated with adult T-cell leukaemia/lymphoma. Transmissible rather than inherited.

Where OnKommon fits

These are the services most often relevant to this cancer. Which of them applies is a clinical question, not an automatic one.

Signature BLL+Comprehensive lymphoid profiling, 600+ genes.See how it works Signature BML+Comprehensive myeloid profiling, 600+ genes.See how it works Blueprint CareThe decision report that reads the profile and ranks the options.See how it works DecipherReinterprets sequencing already done elsewhere, without repeating it.See how it works

This entry is educational. It describes what is commonly discussed in this cancer, not what should happen for any individual. Which of it applies depends on the specific diagnosis, stage, prior treatment and the person themselves. Nothing here is a recommendation, and no list of biomarkers here is exhaustive. Decisions belong with a treating team who know the whole case.

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