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Grading and classifying stomach cancer
To find out the grade of stomach cancer, the pathologist looks at a tissue sample from the stomach under a microscope. The pathologist gives stomach cancer a grade from 1 to 4. The lower the number, the lower the grade.
The grade is a description of the differentiation of the cancer cells. Differentiation is how the cancer cells look and behave compared to normal cells.
Low grade means that the cancer cells are well differentiated. They look and act much like normal cells. Lower grade cancer cells tend to be slow growing and are less likely to spread.
High grade means that the cancer cells are poorly differentiated, or undifferentiated. They look and act less normal, or more abnormal. Higher grade cancer cells tend to grow more quickly and are more likely to spread.
Knowing the grade gives your healthcare team an idea of how quickly the cancer may be growing and how likely it is to spread. This helps them plan your treatment. The grade can also help the healthcare team predict how you might respond to treatment.
Classifying stomach cancer
There are several classification systems used for stomach cancer around the world. In Canada, 2 main classification systems are used.
The Lauren classification is based on how the gastric tissue looks and behaves when examined under a microscope. This is the system most often used to describe how adenocarcinoma tumours, the most common type of stomach cancer, look and behave.
The Lauren classification divides adenocarcinoma of the stomach into 2 main types:
- intestinal type – Tumour cells are well differentiated, grow slowly and tend to form glands. This type is found more often in men than in women and occurs more often in older people.
- diffuse type – Tumour cells are poorly differentiated, behave aggressively and tend to scatter throughout the stomach (rather than form glands). This type spreads to other parts of the body (metastasizes) much quicker than intestinal type tumours. The diffuse type occurs equally among men and women and tends to develop at a younger age than the intestinal type.
In this system there may also be a mixed type of adenocarcinoma of the stomach, made up of both intestinal and diffuse types.
The World Health Organization (WHO) classification goes into more detailed groups than the Lauren classification. There are 5 main types of stomach cancer in the WHO classification.
- tubular adenocarcinoma – This is made up of different sized small branching tubes (tubules).
- papillary adenocarcinoma – This tumour grows outward from the stomach wall and contains finger-like growths that stick out into the stomach cavity. The cells tend to look and behave much like normal cells.
- mucinous adenocarcinoma – There is a lot of mucin (the main substance in mucus) outside of the cancer cells.
- poorly cohesive carcinomas (including signet ring cell carcinoma and others) – These are arranged into clumps of cancerous cells.
- mixed carcinoma – This contains a mix of types of adenocarcinomas of the stomach.