In a patient with polyclonal T‑cell receptor gamma (TRG) gene rearrangements where each clone is less than 2.5% of total sequencing reads, does this exclude T‑cell lymphoma and require any further evaluation?

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Last updated: September 17, 2026 • View editorial policy

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Polyclonal TRG Gene Rearrangements Below 2.5% Do Not Exclude T-Cell Lymphoma

A polyclonal TRG result with all clones <2.5% of total reads does NOT definitively exclude T-cell lymphoma and requires clinical correlation with histopathology, immunophenotyping, and consideration of repeat biopsy if clinical suspicion remains high.

Understanding the Result

Your molecular result shows multiple TRG gene rearrangements, but none meet the threshold for clonality (all <2.5% of total sequencing reads). According to EuroClonality/BIOMED-2 guidelines, this pattern would be classified as "polyclonality detected" or "no clonality detected" 1. However, this molecular finding must be interpreted within the complete clinical and pathological context.

Why This Doesn't Exclude Lymphoma

Limited Sensitivity in Early Disease

  • Patch-stage mycosis fungoides is particularly problematic: Recent NGS studies show that all 4 non-monoclonal cases in one series were patch-stage disease 2, and the overall sensitivity for detecting clonality in cutaneous T-cell lymphoma ranges from only 71-76% even with advanced techniques 3, 2
  • The clinical sensitivity of TRG analysis for clear-cut, advanced-stage CTCL is only 76%, meaning 24% of proven lymphomas show no detectable clonality 4

Technical Limitations

  • Polyclonal T-cell contamination obscures clones: As little as 30% polyclonal T-cells in a sample can mask a true T-cell clone 5
  • Sampling issues: The malignant clone may not be adequately represented in the specific tissue section analyzed
  • Detection threshold: Most methods require approximately 1-6% clonal T-cells against a polyclonal background for detection 6, 4

The TRG Gene's Inherent Problem

The TRG gene has a very limited V region repertoire (only 8-10 rearranging Vγ genes), which creates pseudoclonality even in polyclonal populations 5. This means normal polyclonal T-cells can produce patterns that mimic oligoclonality, but conversely, true clones can be hidden within apparently polyclonal backgrounds.

Required Further Evaluation

Immediate Steps:

  1. Correlate with histopathology: Review architectural features, cytologic atypia, epidermotropism, and Pautrier microabscesses
  2. Immunophenotyping: Look for aberrant T-cell marker loss (CD2, CD3, CD5, CD7) or abnormal CD4:CD8 ratios
  3. Clinical assessment: Evaluate for patch/plaque morphology, distribution, chronicity, and treatment response

When to Pursue Additional Testing:

  • Strong clinical/histologic suspicion persists: Consider repeat biopsy from a different or more developed lesion
  • Multiple biopsies over time: Serial sampling may capture clonal evolution as disease progresses 2
  • Consider alternative molecular targets: TCRB gene rearrangement analysis may detect clonality missed by TRG 1

Critical Pitfalls to Avoid

⚠️ Do not use molecular results alone to rule out lymphoma - The EuroClonality guidelines explicitly state that molecular clonality conclusions must be integrated with clinical and histopathological findings 1

⚠️ Beware of false reassurance in early-stage disease - Patch-stage MF has the lowest molecular detection rate and remains a diagnostic challenge even with NGS 2

⚠️ Recognize that "polyclonal" doesn't mean "benign" - Even proven T-cell lymphomas can show polyclonal patterns due to technical limitations, sampling issues, or overwhelming reactive T-cell populations 5, 4

The Bottom Line

Your result indicates no detectable clonal T-cell population by current molecular standards, but this has insufficient negative predictive value to exclude T-cell lymphoma. The diagnosis requires synthesis of clinical presentation, histopathology, immunophenotyping, and molecular data. If clinical suspicion remains high despite this polyclonal result, proceed with close clinical follow-up and consider repeat biopsy from evolving lesions rather than accepting this single molecular result as definitive exclusion of malignancy.

References

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