Gastric cancer (GC) is the 4th deadliest cancer worldwide in 2020 according to the WHO. Poor patient prognosis is attributed to late-stage diagnosis and lack of effective treatments. Diffuse-type GC (DGC) is a morphologically subtle, relatively spontaneous, and aggressive form of GC. My thesis work investigates a novel method of DGC early detection using stool biomarkers and identifying inhibitors of CD44+ GC stem-like cells to treat GC. I validated a novel method of detecting DGC through measuring stool biomarkers in a mouse model of GC and in stool obtained from patients with hereditary DGC. The proteome and microbiome of stool in the context of GC was compared to that from healthy stool, and potential protein and microbial biomarkers were identified. Stool protein biomarkers were correlated to disease progression by immunoblot assays which validated a panel of proteins: actinin alpha 4, neutral ceramidase (ASAH2), dipeptidyl peptidase 4, valosin-containing protein, lactotransferrin, and tropomyosin-2. These biomarkers were demonstrated to be upregulated in stomach tumors compared to healthy tissue. ASAH2 was previously unassociated with GC tumorigenesis, and I characterized its importance in GC cell line viability using chemical inhibition which was reversed by sphingosine and S1P supplementation. CD44 has been identified as a marker of GC stem-like cancer cells which promote disease initiation and aggressiveness. However, this has not been characterized in an autochthonous mouse model. I introduced a deletion of CD44 in our lab’s genetically engineered mouse model of GC (TCON) which resulted in increased lifespan and reduced metastasis. Next, I tested a library of FDA approved and bioactive compounds against CD44 enriched AGS GC cells. I validated a panel of molecules more effective than frontline therapeutic 5-fluorouracil. Some of the effective compounds were those which targeted the mitochondrial apoptosis pathway, de-ubiquitinase 14, and HDACs. In conclusion, my thesis work discovers a novel method of GC detection through stool biomarkers and proposes some therapeutic strategies for GC treatment focused on CD44+ GC stem-like cells.