Michael C. Heinrich, MD, OHSU Knight Cancer Institute, Portland, OR, explores the use of immunotherapy in patients with gastrointestinal stromal tumors (GISTs), touching on strategies to increase the immunogenicity of the tumor microenvironment in order to improve the number of prolonged responses. Dr Heinrich also outlines the impact of tyrosine kinase inhibitors on responses to immune checkpoint blockade as evaluated in in vivo models. This interview took place at the American Society of Clinical Oncology (ASCO) 2022 Annual Meeting in Chicago, IL.

In this video, we will discuss the pathology of Gastro intestinal Stromal Tumor or GIST

.

Chapters

0:00 Introduction
0:54 Symptoms of Gastrointestinal stromal tumors
1:36 Survival rate of Gastrointestinal stromal tumors
2:07 Diagnosis of Gastrointestinal stromal tumors
2:53 Treatment of Gastrointestinal stromal tumors
3:31 Causes of Gastrointestinal stromal tumors




Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. GISTs arise in the smooth muscle pacemaker interstitial cell of Cajal, or similar cells.[2] They are defined as tumors whose behavior is driven by mutations in the KIT gene (85%),[2] PDGFRA gene (10%),[2] or BRAF kinase (rare).[2] 95% of GISTs stain positively for KIT (CD117).[2][3] Most (66%) occur in the stomach and gastric GISTs have a lower malignant potential than tumors found elsewhere in the GI tract.[3]
Classification

GIST was introduced as a diagnostic term in 1983.[2]:1060 Until the late 1990s, many non-epithelial tumors of the gastrointestinal tract were called "gastrointestinal stromal tumors". Histopathologists were unable to specifically distinguish between types we now know to be dissimilar molecularly. Subsequently, CD34, and later CD117 were identified as markers that could distinguish the various types.[citation needed] Additionally, in the absence of specific therapy, the diagnostic categorization had only a limited influence on prognosis and therapy.

The understanding of GIST biology changed significantly with identification of the molecular basis of GIST,[2]:1065 particularly c-KIT. Historically, literature reviews prior to the molecular definition of GIST, and for a short time thereafter, asserted that 70-80% of GISTs were benign.[4][5][6] The identification of a molecular basis for GIST led to the exclusion of many tumors that had been considered as GIST previously, and also the incorporation of a much larger number of tumors that had been labeled as other types of sarcomas and undifferentiated carcinomas.[2]:1065 For example, some previous diagnoses of stomach and small bowel leiomyosarcomas (malignant tumor of smooth muscle) would be reclassified as GISTs on the basis of immunohistochemical staining. All GIST tumors are now considered to have malignant potential, and no GIST tumor can be definitively classified as "benign".[7] Hence, all GISTs are eligible for cancer staging in the AJCC (7th edition) / UICC.[8] Nonetheless, different GISTs have different risk assessments of their tendency to recur or to metastasize, dependent on their site of origin, size, and number of mitotic figures.

Due to the change in definition, clinical pathways of care before the year 2000 are largely uninformative in the current era.[2]
Signs and symptoms
GISTs may present with trouble swallowing, gastrointestinal bleeding, or metastases (mainly in the liver).Intestinal obstruction is rare, due to the tumor's outward pattern of growth. Often, there is a history of vague abdominal pain or discomfort, and the tumor has become rather large by time the diagnosis is made.