From the Guidelines
Gastrointestinal Stromal Tumors (GISTs) of the stomach have a relatively low likelihood of metastasizing to the ribs specifically, with bone metastases, including to the ribs, occurring in only about 1-6% of metastatic GIST cases. When GISTs metastasize, they most commonly spread to the liver (approximately 50-65% of metastatic cases) and the peritoneum (approximately 20-40%) 1. The risk of metastasis increases with larger tumor size (especially >5cm), higher mitotic rate (>5 mitoses per 50 high-power fields), and certain genetic mutations (particularly those in exon 11 of the KIT gene) 1.
Key Factors Influencing Metastasis
- Tumor size: larger tumors are more likely to metastasize
- Mitotic rate: higher rates indicate a greater risk of metastasis
- Genetic mutations: certain mutations, such as those in exon 11 of the KIT gene, increase the risk of metastasis
Treatment and Monitoring
Treatment for metastatic GIST typically involves tyrosine kinase inhibitors like imatinib (starting at 400mg daily), with sunitinib or regorafenib as second and third-line options respectively if resistance develops 1. Regular monitoring with CT scans every 3-6 months is recommended to assess treatment response. The rarity of rib metastases from stomach GISTs is due to the tumor's biological behavior, as it tends to spread via direct extension or through the bloodstream primarily to the liver rather than to distant bone sites.
Clinical Implications
Given the low likelihood of rib metastasis, clinicians should prioritize monitoring for more common sites of metastasis, such as the liver and peritoneum, while also being aware of the potential for rare metastatic sites, including the ribs. This approach will help optimize treatment outcomes and improve patient quality of life.
From the FDA Drug Label
The primary objective of the two studies was to evaluate either progression-free survival (PFS) with a secondary objective of overall survival (OS) in one study or overall survival with a secondary objective of PFS in the other study. A planned analysis of both OS and PFS from the combined datasets from these two studies was conducted. Results from this combined analysis are shown in Table 26 Table 26: Overall Survival, Progression-Free Survival and Tumor Response Rates in the Phase 3 GIST *Trials * Abbreviation: GIST, gastrointestinal stromal tumors. Imatinib Mesylate 400 mg N = 818 Imatinib Mesylate 800 mg N = 822 Progression-Free Survival (months) Median 18.9 23.2 95% CI 17.4–21.2 20.8–24.9 Overall Survival (months) 49 48.7 95% CI 45.3–60 45.3–51. 6 Best Overall Tumor Response Complete Response 43 (5.3%) 41 (5%) Partial Response 377 (46.1%) 402 (48.9%)
The FDA drug label does not answer the question.
From the Research
Likelihood of GIST Stomach Tumor Metastasis to Ribs
- The likelihood of a Gastrointestinal Stromal Tumor (GIST) stomach tumor metastasizing to the ribs is considered rare, as GISTs most commonly metastasize to the liver and abdominal cavity 2.
- Distant metastases to other sites, especially to the bones, are relatively rare, but a case report describes a 62-year-old man with metastatic spread of GIST to the skull, ribs, and both sacroiliac joints 2.
- The role of surgery in metastatic GIST is considered in patients who respond to imatinib, particularly if a R0/R1 resection is achieved, but the benefit of surgery in patients with focal tumor progression on imatinib is unclear 3.
- GISTs are the most common type of gastrointestinal mesenchymal tumors, and metastasis to the perigastric lymph nodes is relatively rare, compared with liver or peritoneal metastasis 4.
- FDG PET and FDG PET/CT imaging are valuable in the diagnostic work-up of patients with GISTs, including initial disease evaluation, detection of tumor recurrence, and early assessment of treatment response to molecularly targeted agents 5.
- Surgical excision is the definitive treatment for all primary GISTs greater than 2 cm without evidence of peritoneal seeding or metastasis, and achieving negative microscopic margins is important, although the importance of this is controversial 6.