Tumor of the stomach

Generally speaking, all cells grow and divide in order to help the organism grow larger, or to replace dead or damaged cells. Depending on the type of cell, they either go through mitosis or meiosis, creating diploid or haploid daughter cells, respectively. In cells that complete mitosis, after they divide, they enter a phase called interphase. Interphase is the longest part of the cell cycle and is composed of G1, S, and G2 phases. During this time, the cell completes a series of growth, DNA replication, and more growth to ensure they are ready to divide again eventually.[3]

In order to make sure that this cycle runs smoothly, there are a series of checkpoints that the cell reaches to ensure that DNA replication has been completed correctly and that the cell is of correct size.[4] These checkpoints include an un-replicated DNA checkpoint, a spindle assembly checkpoint, a chromosome-segregation checkpoint, and various DNA damage checkpoints.[5] Table 1 below describes different cell cycle checkpoints and their various purposes.

In mammalian organisms, the cell cycle is regulated through interactions of cyclin-dependent kinases (CDKs) and cyclins.[4] CDKs are always present in the cell, while cyclins are in a constant cycle of degradation and synthesis. Although CDKs are always present in a cell, their natural state is in the inactive form, which is where the cyclins come into play. In a normal cell, each phase of the cell cycle will produce unique types of cyclins which bind to specific cyclin-dependent kinases at each checkpoint. Once they are bound, the complex is now activated and the CDK is able to proceed with phosphorylation.

Checkpoints that monitor for DNA damage are regulated in a slightly different manner. They still involve the use of cyclins and CDKs, but they also involve the use of a transcription factor called p53, a crucial part of cell cycle regulation. In a cell where everything has proceeded normally, p53 will be degraded and have essentially no function. If, however, there is any damage, p53 will become stabilized, allowing it to bind to the damaged DNA.[5] In this case, the cell cycle will halt long enough for the damage to be repaired, or if the damage is severe enough, the cell will undergo apoptosis.

This image depicts the division of normal cells versus the division of cancerous cells.[6]

In the case of tumors, the cells display a level of abnormal growth. In most cases, this abnormal growth comes from an error in the cell cycle checkpoints. There are three general errors that occur within the cell cycle to cause abnormal cell growth. The first error is unscheduled proliferation, essentially refers to the cell continuing to grow and divide without the proper signaling from mitosis. Genomic instability, the second error, refers to mutations within the genome which causes errors in the replication or repair of the gene. Lastly, chromosomal instability is caused by mutations which disrupt the normal segregation of chromosomes in mitosis or meiosis.[4] Although caused by different abnormalities, each of these errors is in some way mediated by a mistake in cyclin-dependent kinases. In a healthy cell, the interactions between cyclins and cyclin-dependent kinases are essential for either halting the cell cycle or allowing the cell to continue through a checkpoint. In abnormal cells, however, acquired mutations allow the cells to bypass these checkpoints by deregulating the cyclins and CDKs, even if there have been significant errors.[7]

A microscopic view of stomach lining containing goblet cells, parietal cells, chief cells, and enteroendocrine cells.[9]

Unfortunately, the early anatomical changes in the lining of the stomach that lead to cancer are rarely noticeable. The lining of the stomach is made up of a simple columnar epithelium which folds into what are called gastric glands. Within these glands are four different cell types: goblet cells, parietal cells, chief cells, and enteroendocrine cells.[10] Mutations in any of these cell types can begin the process of uncontrolled cell proliferation, ultimately leading to the formation of a tumor. It is also important to note that depending on where in the stomach the tumor starts, signs and symptoms as well as treatment options may differ.

1. Adenocarcinoma
2. Primary Gastric Lymphoma
3. Gastrointestinal Stromal Tumor (GIST)
4. Neuroendocrine (Carcinoid) Tumors

• Smoking
• Helicobacter pylori infection.
• Diet low in fruits and vegetables.
• Diet high in salt and nitrates.
• Polyps
• Genetic alterations - p53 mutation, micro-satellite instability, E-cadherin gene
• Previous radiation
• Pernicious anaemia

• Dysphagia
• Indigestion
• Nausea
• Vomiting
  • Vomiting blood
• Abdominal pain
• Loss of appetite
• Abdominal swelling
• Passing black stool