John L. Marshall, MD
Oncologists have been slow to introduce targeted and immune therapies into the treatment of gastrointestinal (GI) cancers, but that is changing, and poor patient survival statistics call for a continuation of this trend, according to John L. Marshall, MD, chief of the Division of Hematology and Oncology and a professor of medicine and oncology at Georgetown Lombardi Comprehensive Cancer Center in Washington, DC.
In remarks at the 3rd Annual School of Gastrointestinal Oncology
), held in New York, New York, in April, Marshall described a push to differentiate gastrointestinal cancer types based on tumor mutational load (TML) or tumor mutational burden (TMB), mismatch repair deficiency (dMMR) status, microsatellite instability (MSI) status, and protein expression. Although testing for these biomarkers has become prevalent for other tumor sites, cancers of the stomach and intestines still tend to be lumped together into a single category, adding to misconceptions on how to classify and treat.
Marshall explained that gastric cancers are distinct diseases based on their molecular subtypes and should be treated differently. Clinically, treating these tumors the same produces mixed results, he said.
It is clear that upper GI cancers can be sorted by their anatomic locations and then by pathology. Knowledge of molecular subtypes has added a third tier of sorting, Marshall said. “It makes more sense to use [molecular distinctions] than the right versus left colon. A long time ago, we treated all of these squamous and adeno carcinomas and all of the locations as 1 set of cancers, and clearly we’re dividing it up.” Molecular stratification into subgroups leads to more accurate classification of tumors, better treatment strategies, and, ultimately, better survival rates.
Although the overall estimated incidence of gastric cancers has declined by about 2.3% from 1995 to 2013 and survival rates are increasing, the numbers still “aren’t that great,” Marshall said, adding that for patients younger than 50 years, the incidence of gastric cancers increased by 1.3% annually during that same period.1 Assessing each patient for molecular biomarkers could help physicians make better decisions about therapy.
Each actionable biomarker represents a strong case for classifying gastric and upper GI tumors differently. HER2 expression has significant value in characterizing gastric tumors, Marshall noted. “We know that HER2 expression in this disease is much more common in the proximal cancers and almost unheard of in squamous cancers.”
Among all gastric cancers, HER2 expression is found in 17.9% of tumors. In gastroesophageal junction (GEJ) tumors, it is found at a considerably higher rate: 25% to 34% of tumors. In chromosomal instable gastric tumors, HER2 expression is 16% to 34%; in genomically stable tumors, 6% to 7%.
In a comparative molecular analysis of esophageal squamous cell carcinoma, esophageal adenocarcinoma, and gastric adenocarcinoma using next-generation sequencing (NGS), investigators demonstrated that each type of gastric tumor has different expression of various genes.2 “There are some common threads,” Marshall said, “but there is differential expression.”
GEJ adenocarcinoma had higher expression of CDH1 and RNF43
mutations than esophageal adenocarcinoma and squamous cell esophageal cancer. GEJ adenocarcinoma and esophageal adenocarcinoma tumors had relatively high levels of ARID1A
mutations. Squamous cell esophageal cancer tumors had higher incidence of KMT2D, PIK3CA, SETD2, NOTCH1, PTEN, RB1, FOXO3, BRCA1,
than the other 2 disease types. All 3 tumor types had high levels of TP53
Protein expression screened by immunohistochemistry (IHC) testing also distinguished these tumors from each other in the analysis. All tumors had high expressions of EGFR, with squamous cell esophageal cancer running the highest. Squamous cell esophageal cancer also had higher expression of ERCC1, PD-L1, RRM1, TLE3, TOPO1, and TUBB3.
Table. Mutational Expression in Diffuse and Intestinal Gastric Cancers2
There is also a statistically significant difference between diffuse and intestinal tumors based on NGS testing in the analysis (Table
). “We recognize diffuse and intestinal [tumors] as different anatomically, but we don’t treat them differently clinically,” Marshall said. This distinction persists in IHC testing, where intestinal tumors have higher expressions of HER2, TOP2A, TS, RRM1, and cMET.