The stomach adenocarcinoma proteome

Stomach cancer, also termed gastric cancer or gastric carcinoma, is the fifth most common cancer in the world and the fourth leading cause of cancer-related mortality. The global 5-year survival rate is 20%. Stomach cancer occurs most often in men over the age of 40 and is common in Japan, Chile, and Iceland. The main risk factor for developing this type of cancer is Helicobacter pylori infection. Other risk factors include a history of adenomatous gastric polyps, chronic atrophic gastritis or pernicious anemia as well as smoking and consumption of salted, cured or smoked foods. A genetic component is present in approximately 10% of all cases.

Stomach cancer originates from the mucosa of the stomach and consist of adenocarcinoma of varying architecture, grade of differentiation and mucin content. Clinical classification into different stages is necessary for determining the most suitable therapy. Tumors restricted to the stomach and with no metastasis are treated with a combination of surgery, chemotherapy, radiotherapy and/or target therapy. Metastasized tumors are not curable and associated with more dismal prognosis.

Here, we explore the stomach adenocarcinoma proteome using TCGA transcriptomics data and antibody-based protein data. 324 genes are suggested as prognostic based on transcriptomics data from 346 patients; 254 genes are associated with unfavorable prognosis and 70 genes are associated with favorable prognosis.

TCGA data analysis

In this metadata study, we used data from TCGA where transcriptomics data was available from 346 patients in total, 123 females and 223 males. A majority of the patients (203 patients) were still alive at the time of data collection. The stage distribution was stage i) 45 patients, stage ii) 110 patients, stage iii) 143 patients, stage iv) 34 patients and 14 patients with missing stage information.

Unfavorable prognostic genes in stomach adenocarcinoma

For unfavorable genes, higher relative expression levels at diagnosis give significantly lower overall survival for the patients. There are 254 genes associated with an unfavorable prognosis in stomach adenocarcinoma. In Table 1, the top 20 most significant genes related to an unfavorable prognosis are listed.

ITGAV is a gene associated with an unfavorable prognosis in stomach adenocarcinoma. The best separation is achieved by an expression cutoff at 28 TPM which divides the patients into two groups with 19% 5-year survival for patients with high expression versus 51% for patients with low expression, p-value: 4.51e-5. Immunohistochemical staining using an antibody targeting ITGAV (CAB002499) shows a differential expression pattern in stomach adenocarcinoma samples.

p<0.001 0.00.10.20.30.40.50.60.70.80.91.0 0 1 2 3 4 5 6 7 8 910
ITGAV - survival analysis

ITGAV - high expression

ITGAV - low expression

Table 1. The 20 genes with highest significance associated with an unfavorable prognosis in stomach adenocarcinoma.

Gene
Description
Predicted location
mRNA (cancer)
p-value
Prognostic
MAGED4B MAGE family member D4B Membrane, Intracellular 2.7 1.68e-5 potential
SLCO2A1 Solute carrier organic anion transporter family member 2A1 Membrane 17.2 7.46e-5 potential
BLMH Bleomycin hydrolase Intracellular 15.2 1.49e-4 potential
EPM2A EPM2A glucan phosphatase, laforin Intracellular 2.2 1.64e-4 potential
MARCKS Myristoylated alanine rich protein kinase C substrate Intracellular 48.1 2.07e-4 potential
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Favorable prognostic genes in stomach adenocarcinoma

For favorable genes, higher relative expression levels at diagnosis give significantly higher overall survival for the patients. There are 70 genes associated with a favorable prognosis in stomach adenocarcinoma. In Table 2, the top 20 most significant genes related to a favorable prognosis are listed.

CLDN7 is a gene associated with a favorable prognosis in stomach adenocarcinoma. The best separation is achieved by an expression cutoff at 47 TPM which divides the patients into two groups with 38% 5-year survival for patients with high expression versus 24% for patients with low expression, p-value: 6.03e-4. Immunohistochemical staining using an antibody targeting CLDN7 (HPA014703) shows a differential expression pattern in stomach adenocarcinoma samples.

p<0.001 0.00.10.20.30.40.50.60.70.80.91.0 0 1 2 3 4 5 6 7 8 910
CLDN7 - survival analysis

CLDN7 - high expression

CLDN7 - low expression

Table 2. The 20 genes with highest significance associated with a favorable prognosis in stomach adenocarcinoma.

Gene
Description
Predicted location
mRNA (cancer)
p-value
Prognostic
BRI3BP BRI3 binding protein Membrane 21.8 1.51e-4 potential
CLSPN Claspin Intracellular 4.4 4.07e-4 potential
DEGS2 Delta 4-desaturase, sphingolipid 2 Membrane, Intracellular 22.7 5.48e-4 potential
NCLN Nicalin Membrane, Intracellular 43.1 6.44e-4 potential
TMEM164 Transmembrane protein 164 Membrane 16.3 7.80e-4 potential
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The stomach adenocarcinoma transcriptome

The transcriptome analysis shows that 72% (n=14604) of all human genes (n=20162) are expressed in stomach adenocarcinoma. All genes were classified according to the stomach adenocarcinoma-specific expression into one of five different categories, based on the ratio between mRNA levels in stomach adenocarcinoma compared to the mRNA levels in the other 16 analyzed cancer tissues.

Figure 1. The distribution of all genes across the five categories based on transcript abundance in stomach adenocarcinoma as well as in all other cancer tissues.

214 genes show some level of elevated expression in stomach adenocarcinoma compared to other cancers (Figure 1). The elevated category is further subdivided into three categories as shown in Table 3.

Table 3. The number of genes in the subdivided categories of elevated expression in stomach adenocarcinoma.

Distribution in the 31 cancers
Detected in singleDetected in someDetected in manyDetected in all Total
Specificity
Cancer enriched 5800 13
Group enriched 050485 103
Cancer enhanced 19303811 98
Total 24888616 214

Additional information

Stomach cancer is commonly diagnosed based on biopsy obtained through gastroscopy. Gastroscopy entails the insertion of a fiber optic camera into the stomach to examine the gastric mucosa and more easily collect biopsy samples. In Stage 0, the cancer is limited to the inner lining of the stomach and this early stage is treatable by endoscopic mucosal resection, or by gastrectomy and lymphadenectomy without a need for chemotherapy or radiation. Stage I tumors penetrate to the second or third layers of the stomach (IA) or to the second layer and nearby lymph nodes (IB). Stage IA is treated by surgery and Stage IB may in addition to surgery, be treated with chemotherapy (5-fluorouracil) and radiation therapy. In Stage II, the tumor penetrates to the second layer of the stomach and involve more distant lymph nodes. Patients with stage II receive the same treatment as for Stage I tumors, sometimes with the addition of neoadjuvant chemotherapy. Stage III is characterized by penetration to the third layer and metastases in more distant lymph nodes and is treated in the same way as stage. Stage IV involved spread to adjacent tissues or metastasis to distant organs. A cure is very rarely possible at this stage and treatment to prolong life or reduce symptoms may be implemented, including laser treatment, chemotherapy, surgery, and/or stents to keep the digestive tract open.

There are four major histologic types of stomach cancers: tubular, papillary, mucinous and poorly cohesive carcinoma (including signet-ring cell carcinomas). Tubular and papillary adenocarcinomas are the most common histological type of early stomach cancer. The tubular type is composed of irregular glands that form fused or branched tubules and papillary carcinoma are characterized by epithelial projections. Mucinous adenocarcinoma accounts for 10% of gastric cancers and typically shows extracellular pools of mucin. Signet-ring cell carcinomas consist of mucin containing cells. In immunohistochemical assays 50% of stomach cancers express cytokeratin 7 and 75% are positive for cytokeratin 20. Stomach cancer is discriminated from metastatic colorectal cancer by showing SATB2 negative immunohistochemical results.

Relevant links and publications

Uhlen M et al., A pathology atlas of the human cancer transcriptome. Science. (2017)
PubMed: 28818916 DOI: 10.1126/science.aan2507

Cancer Genome Atlas Research Network et al., The Cancer Genome Atlas Pan-Cancer analysis project. Nat Genet. (2013)
PubMed: 24071849 DOI: 10.1038/ng.2764

Uhlén M et al., Tissue-based map of the human proteome. Science (2015)
PubMed: 25613900 DOI: 10.1126/science.1260419

Gremel G et al., The human gastrointestinal tract-specific transcriptome and proteome as defined by RNA sequencing and antibody-based profiling. J Gastroenterol. (2015)
PubMed: 24789573 DOI: 10.1007/s00535-014-0958-7

Histology dictionary - Stomach cancer