Pathological complete response in advanced gastrointestinal stromal tumor after imatinib therapy

Pathologic complete response to neoadjuvant imatinib of a gastric stromal tumor with concomitant mutations in KIT: A case report and literature review

Key clinical message

We report the first case of pathologic complete response (pCR) to neoadjuvant imatinib in a gastric stromal tumor harboring KIT mutations in both exons 11 and 9. The significance of this co-occurrence is unknown and might increase the responsiveness of gastrointestinal stromal tumors (GISTs) to imatinib.

Abstract

pCR of GIST to neoadjuvant imatinib is rare. We report a case of pCR to neoadjuvant imatinib in a gastric stromal tumor that harbored co-occurrence of multiple KIT mutations in exons 11 and 9. This co-occurrence in exons 9 and 11 is the first to be reported in the English literature.

A literature review and database of how the primary KIT/PDGFRA variant of a gastrointestinal stromal tumour predicts for sensitivity to imatinib

It is well recognized that the primary KIT or PDGFRA variant of a gastrointestinal stromal tumour (GIST) can predict sensitivity to imatinib. However, these data are currently spread across a wide range of publications and have not been collated as one reference. A broad-ranging literature search was therefore performed to assemble such a database which should help optimize imatinib-based management of GIST patients henceforth. Having excluded wild type GISTs and results for imatinib used as adjuvant therapy, 79 publications (dated August 2001 to March 2022) underwent data extraction. These data on imatinib sensitivity were either derived from in vitro studies, predicted by in silico analysis or based on in vivo clinical patient response. Data interpretation carried some caveats: there was a potential for replication of patient-derived data between older and new publications; only predicted protein sequences were presented; the criteria used to record clinical response were not uniform across all publications; and imatinib dosage could vary between different clinical publications. However, these data showed broad agreement of imatinib sensitivity amongst similar subtypes of KIT or PDGFRA variant. There was also agreement between in vivo versus in vitro/in silico derived sensitivity data for most variants when both data types were available.

Pathologic complete response with neoadjuvant imatinib for locally advanced pelvic GIST

There are few data that show pathologic complete response (pCR) to imatinib treatment in gastrointestinal stromal tumors (GISTs). We describe a case of a patient with pCR of a pelvic, locally advanced, high-risk GIST who was treated with neoadjuvant imatinib and ultimately underwent a conservative procedure. A 48-year-old male presented with a pelvic mass 10 cm in diameter. Biopsy revealed a gastrointestinal stromal tumor of rectal origin. Although it was considered initially resectable, an extensive procedure would have been necessary for complete resection. Treatment with imatinib was initiated, resulting in partial response. The patient remained on imatinib for over 15 months, maintaining stable disease. Radical prostatectomy with anal sphincter preservation was performed. Pathological report revealed no viable neoplastic cells. The use of imatinib was held for 6 months after the surgery. At a follow-up 15 months after surgery, the patient had no evidence of disease. Our report may help to guide future studies of neoadjuvant imatinib for large pelvic or rectum GISTs that are initially considered unresectable.

Role of c-kit/SCF in cause and treatment of gastrointestinal stromal tumors (GIST)

c-Kit encodes for the receptor tyrosine kinase (RTK) and belongs to type III receptor family. This includes platelet derived growth factor (PDGF) alpha and beta and macrophage colony stimulating factor (mCSF) apart from others. Their characteristic features are the presence of five immunologlobulin like domains in the extracellular region and 70-100 residues long kinase insert domain in the cytoplasmic region. The RTKs activate several signaling pathways within the cells leading to cell proliferation, differentiation, migration or metabolic changes. The Kit ligand-stem cell factor (SCF) induces a rapid and complete receptor dimerization resulting in activation by autophosphorylation of the catalytic tyrosine kinase and generation of signal transduction leading to regulation of cell growth. Various mutations in c-kit such as insertions and deletions (without affecting reading frame) and point mutations in the inhibitory juxtamembrane (JM) domain encoded by exon 11 have been reported in gastrointestinal stromal tumors (GISTs). Thus, c-kit signaling is believed to play a role in tumorigenesis. Efforts are being made to control and treat these tumors by blocking kit signaling using Imatinib with varying degrees of success. This review deals with the features of c-kit, its ligand and roles in gastrointestinal stromal tumors.

The role of PDGF in radiation oncology

Platelet-derived growth factor (PDGF) was originally identified as a constituent of blood serum and subsequently purified from human platelets. PDGF ligand is a dimeric molecule consisting of two disulfide-bonded chains from A-, B-, C- and D-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors. PDGF is a potent mitogen and chemoattractant for mesenchymal cells and also a chemoattractant for neutrophils and monocytes. In radiation oncology, PDGF are important for several pathologic processes, including oncogenesis, angiogenesis and fibrogenesis. Autocrine activation of PDGF was observed and interpreted as an important mechanism involved in brain and other tumors. PDGF has been shown to be fundamental for the stability of normal blood vessel formation, and may be essential for the angiogenesis in tumor tissue. PDGF also plays an important role in the proliferative disease, such as atherosclerosis and radiation-induced fibrosis, regarding its proliferative stimulation of fibroblast cells. Moreover, PDGF was also shown to stimulate production of extracellular matrix proteins, which are mainly responsible for the irreversibility of these diseases. This review introduces the structural and functional properties of PDGF and PDGF receptors and discusses the role and mechanism of PDGF signaling in normal and tumor tissues under different conditions in radiation oncology.

Gastrointestinal stromal tumours: clinical overview, surgery and recent advances in imatinib mesylate therapy

AIMS

To review the clinical features of gastrointestinal stromal tumours (GISTs), the role of surgery and its principles and molecular targeted therapies.

METHODS

A Medline-based literature search on relevant topics was performed in PubMed for key articles concerning the clinical features, biology and the novel strategies in the management, whether surgical and/or pharmaceutical, of gastrointestinal stromal tumours. Some information was obtained from Proceedings of the American Society for Clinical Oncology published recently.

RESULTS

Surgical resection, the first-line intervention for operable GISTs, was historically the only effective treatment. For residual, metastatic and/or inoperable disease, treatment options remain under intense and continuous scrutiny. However, their molecular genetics, i.e. the mutations of the genes coding for KIT or platelet-derived growth factor receptor alpha, two receptor tyrosine kinases, have been targeted for therapeutic intervention by imatinib mesylate -- a tyrosine kinase inhibitor.

CONCLUSION

Treatment of GISTs with imatinib has led to dramatic improvements in progression-free and overall survival, thereby rendering its use in the preoperative and postoperative treatment under intense investigation. New investigational agents are being developed and participation in promising clinical trials remains a standard of care.

GIST under imatinib therapy

The prognosis of patients with a GIST improved significantly since the introduction of imatinib mesylate treatment, leading to disease control in 70% to 85% of patients. The response depends on the presence/ absence and type of mutations in the KIT or Platelet derived growth factor receptor. Unfortunately, we are increasingly faced with the problem of resistance to imatinib treatment, mainly secondary resistance, which by definition occurs after at least 6 months of initial response to the drug. The effects of imatinib on a GIST are still in full exploration and this review focuses upon the available data on the phenotype and genotype of a GIST treated with imatinib. Two settings are elaborated separately, a responding/stable GIST, and a resistant GIST. In addition, the attention will be drawn to remarkable (immuno)phenotypic changes that can occur in a GIST under imatinib treatment.