Mitotic Figure is the Most Important Prognostic Factor for Gastric Leiomyoma
The mitotic figure (mitotic count) is the most important prognostic factor for a gastric leiomyoma with high mitotic figures. 1 According to the ESMO Clinical Practice Guidelines, the mitotic rate is one of the three main prognostic factors in gastrointestinal stromal tumors, along with tumor size and tumor site, with mitotic rate being particularly significant for predicting aggressive behavior.
Understanding Prognostic Factors in Gastric Leiomyoma
The Armed Forces Institute of Pathology risk classification, which is widely used for risk stratification, incorporates:
- Mitotic count - The most critical factor
- Tumor size
- Tumor site (location)
- Tumor rupture (if applicable)
Why Mitotic Figure is Most Important
Looking at the evidence from the ESMO guidelines, we can see that mitotic count has the strongest influence on prognosis 1:
For gastric tumors of the same size (5-10 cm), the difference in risk between low mitotic rate (≤5 per 50 HPFs) and high mitotic rate (>5 per 50 HPFs) is dramatic:
- 3.6% risk of metastasis with low mitotic rate
- 55% risk of metastasis with high mitotic rate
This represents a 15-fold increase in risk based on mitotic rate alone.
Comparison of Prognostic Factors
When comparing the options:
Mitotic figure (B): As demonstrated above, this shows the most dramatic impact on prognosis, with high mitotic rates correlating strongly with aggressive behavior regardless of other factors 1.
Size (A): While size is important, its impact is less pronounced than mitotic rate. For example, a small tumor (<2 cm) with high mitotic rate has a worse prognosis than a larger tumor (2-5 cm) with low mitotic rate 1.
Vascular invasion (C): While significant, vascular invasion is not identified in the guidelines as one of the primary prognostic factors for gastric leiomyoma/GIST 1.
Node invasion (D): Lymph node metastasis is actually uncommon in GISTs, and nodal dissection is not routinely recommended during surgery 1. This makes it a less reliable prognostic indicator.
Risk Stratification Based on Mitotic Count
The ESMO guidelines provide a detailed table showing how mitotic count dramatically affects prognosis 1:
For gastric tumors >10 cm:
- With ≤5 mitoses/50 HPFs: 12% risk of metastasis
- With >5 mitoses/50 HPFs: 86% risk of metastasis
Even for smaller tumors (2-5 cm):
- With ≤5 mitoses/50 HPFs: 1.9% risk (very low)
- With >5 mitoses/50 HPFs: 16% risk (moderate)
Clinical Implications
For a patient with a 9×7 cm gastric wall mass with high mitotic figures:
- This patient falls into the high-risk category (Group 6a in the ESMO classification)
- Expected risk of metastasis or tumor-related death is approximately 55% 1
- Close monitoring and consideration of adjuvant therapy would be warranted
Important Considerations
- Tumor rupture is also a highly unfavorable prognostic factor that can offset other factors 1
- The mitotic index should be expressed as the number of mitoses on a total area of 5 mm² (equivalent to 50 high-power fields) 1
- When using prognostic tools, it's important to recognize that mitotic index and tumor size are non-linear continuous variables 1
In conclusion, while all the factors mentioned contribute to prognosis, the mitotic figure (B) has the strongest and most consistent correlation with aggressive behavior and poor outcomes in gastric leiomyoma.