KRAS and BRAF mutations predict primary resistance to imatinib in gastrointestinal stromal tumors

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Gastrointestinal stromal tumors (GIST) often harbor KIT/PDGFRA mutations leading to constitutive receptor activation.
• Imatinib is a targeted therapy effective against GIST, but primary resistance occurs in some patients.
• The mechanisms underlying primary imatinib resistance in GIST require further investigation.

Purpose of the Study:

• To investigate downstream effector alterations in GIST that may explain primary resistance to imatinib.
• To identify novel mechanisms of resistance beyond KIT/PDGFRA mutations.

Main Methods:

• Analysis of KIT, PDGFRA, KRAS, and BRAF mutations in two independent GIST cohorts.
• In vitro experiments using cell lines with specific mutations treated with imatinib.
• Western blotting to analyze KIT receptor and downstream effector activation.

Main Results:

• Concomitant activating mutations in KRAS (5%) or BRAF (2%) were found in GISTs with KIT/PDGFRA mutations.
• Imatinib effectively inhibited mutated KIT but could not block downstream signaling initiated by RAS-RAF effectors.
• This suggests that RAS-RAF pathway activation bypasses imatinib's inhibitory effect on KIT.

Conclusions:

• Activation of the mitogen-activated protein kinase (MAPK) pathway via RAS-RAF signaling is a potential mechanism for primary imatinib resistance in GIST.
• These findings may explain why a subset of GIST patients with imatinib-sensitive mutations do not respond to treatment.
• Targeting the MAPK pathway could be a future therapeutic strategy for resistant GIST.