The Bloom Richardson (BR) score, also known as the Nottingham Histologic Grade, is a crucial grading system used to assess the aggressiveness of invasive breast cancers, specifically "invasive no-special-type" (formerly known as invasive ductal carcinoma). It provides a numerical score that helps oncologists and patients understand the tumor's differentiation and potential behavior.
Understanding the Bloom Richardson Score
The Bloom Richardson score is a pathology-based grading system that evaluates three key morphologic features of breast cancer cells observed under a microscope. Each feature is assigned a score, and the sum of these scores determines the overall grade of the tumor. The total BR score can range from 3 to 9, indicating varying degrees of tumor differentiation and aggressiveness.
The Three Morphologic Features
As specified in Note 4, the BR score is based on an assessment of:
- Degree of Tubule Formation / Histologic Grade: This feature assesses how well the tumor cells form glandular structures (tubules), similar to normal breast tissue.
- Mitotic Activity: This refers to the rate of cell division within the tumor, indicating how quickly the cancer cells are proliferating.
- Nuclear Pleomorphism / Nuclear Grade of Tumor Cells: This evaluates the size, shape, and uniformity of the tumor cell nuclei, reflecting how abnormal they appear compared to normal cells.
Each of these features is individually scored on a scale from 1 to 3, with 1 being the least aggressive (well-differentiated) and 3 being the most aggressive (poorly differentiated).
How the Bloom Richardson Score is Calculated
The individual scores for tubule formation, nuclear pleomorphism, and mitotic activity are summed to arrive at a total Bloom Richardson score. This total score then corresponds to one of three grades:
Feature Evaluated | Score 1 (Low Aggressiveness) | Score 2 (Moderate Aggressiveness) | Score 3 (High Aggressiveness) |
---|---|---|---|
Tubule Formation | >75% of tumor forming tubules | 10-75% of tumor forming tubules | <10% of tumor forming tubules |
Nuclear Pleomorphism | Small, uniform nuclei | Moderate variation in size and shape | Marked variation, large, irregular nuclei |
Mitotic Activity | Low mitotic count (e.g., 0-5 mitoses/10 HPF*) | Moderate mitotic count (e.g., 6-10 mitoses/10 HPF*) | High mitotic count (e.g., >10 mitoses/10 HPF*) |
*HPF: High Power Field, a common unit for microscopic counting.
Interpreting the Final Score
The sum of the three individual scores (ranging from 3 to 9) determines the overall histologic grade of the breast cancer:
- Grade 1 (Score 3-5): Well-differentiated tumor, indicating slow growth and less aggressive behavior.
- Grade 2 (Score 6-7): Moderately differentiated tumor, representing intermediate growth and behavior.
- Grade 3 (Score 8-9): Poorly differentiated tumor, suggesting fast growth and more aggressive behavior.
This grading system is a critical tool for pathologists and oncologists in determining prognosis and guiding treatment decisions for patients with breast cancer.