What are the tumor budding grades in colorectal carcinoma?

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Tumor Budding Grades in Colorectal Carcinoma

Tumor budding in colorectal cancer is graded using a three-tier system: Bd1 (low) = 0-4 buds, Bd2 (intermediate) = 5-9 buds, and Bd3 (high) = ≥10 buds per 0.785 mm² field at the invasive front. 1

The Three-Tier Grading System

The International Tumour Budding Consensus Conference (ITBCC) 2016 established a standardized three-tier classification system with strong consensus (100% agreement) based on moderate quality evidence 1:

  • Bd1 (Low budding): 0-4 tumor buds per 0.785 mm² 1
  • Bd2 (Intermediate budding): 5-9 tumor buds per 0.785 mm² 1
  • Bd3 (High budding): ≥10 tumor buds per 0.785 mm² 1

Clinical Significance by Grade

The grading system directly correlates with patient outcomes—the more tumor buds present, the worse the prognosis. 2

In pT1 Colorectal Cancer:

  • Bd2 and Bd3 are both associated with increased risk of lymph node metastasis 1
  • Tumor budding is a strong independent predictor of lymph node involvement (strong recommendation, high quality evidence) 1

In Stage II Colorectal Cancer:

  • Bd3 specifically is associated with increased risk of recurrence and mortality 1
  • Tumor budding is a strong independent predictor of survival (strong recommendation, high quality evidence) 1

Prognostic Impact:

  • Marked tumor budding shows significantly worse 5-year cancer-related survival (39%) and recurrence-free survival (53%) compared to mild budding (80%/82%) 3
  • Marked tumor budding is an independent predictor of short cancer-related survival (HR 3.137,95% CI 1.517-6.487) 3

Standardized Assessment Method

The ITBCC 2016 established a rigorous methodology to ensure reproducibility 1:

Step-by-Step Protocol:

  1. Scan 10 separate fields at medium power (10x objective) along the invasive front to identify the "hotspot" with highest tumor bud density 1

    • For pT1 endoscopic resections with <10 fields available, scan all available fields 1

  2. Count tumor buds in the selected hotspot using 20x objective lens 1

    • A tumor bud is defined as a single tumor cell or cluster of ≤4 tumor cells (strong recommendation, high quality evidence) 1

  3. Standardize the count to 0.785 mm² field area 1

    • Use normalization factors if your microscope has different eyepiece field numbers 1
    • The standard field corresponds to a 20x objective with 20mm eyepiece field number diameter 1

  4. Report both the grade AND absolute count (e.g., "Tumor budding: Bd3 (high), count 14 per 0.785 mm²") 1

Critical Methodological Points

The "hotspot" method is strongly recommended (100% consensus, moderate quality evidence) because it better reflects the maximal extent of tumor budding and has been used in the vast majority of outcome-based studies 1. While counting multiple fields may be more representative of the entire invasive front, it can "dilute" the final count in cases with focally abundant tumor buds 1.

Tumor budding is assessed on routine H&E staining (strong recommendation, moderate quality evidence) 1, making it practical for daily diagnostic practice without requiring special immunohistochemical stains.

Common Pitfalls to Avoid

  • Don't confuse tumor budding with tumor grade—these are distinct entities (strong recommendation, high quality evidence) 1
  • Always report the absolute bud count in addition to the grade category to avoid loss of information at borderline cases (e.g., 9 buds [Bd2] vs 10 buds [Bd3] may be biologically similar but fall into different risk categories) 1
  • Ensure proper field standardization—different microscopes require normalization factors to achieve the standard 0.785 mm² field area 1
  • Scan adequate number of fields before selecting the hotspot—don't count the first high-budding field you encounter 1

Integration into Clinical Practice

Tumor budding should be taken into account along with other clinicopathological features in a multidisciplinary setting (strong recommendation, high quality evidence) 1. The ITBCC strongly recommends that tumor budding be included in guidelines and protocols for colorectal cancer reporting (100% consensus, high quality evidence) 1.

This three-tier system allows for practical risk stratification in clinical decision-making, particularly for determining need for additional therapy in pT1 cancers and stage II disease 1.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Research

Tumour budding in solid cancers.

Nature reviews. Clinical oncology, 2021

3
Research

Tumour budding at invasive margins and outcome in colorectal cancer.

Colorectal disease : the official journal of the Association of Coloproctology of Great Britain and Ireland, 2008

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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