Grading for colorectal cancer is mainly done for adenocarcinomas. To find out the grade of a tumour, the pathologist looks at a tissue sample from the colon or rectum under a microscope. 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.
The tumours are often described as low grade or high grade.
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.
The pathologist may also give colorectal cancer a grade from 1 to 4. The lower the number, the lower the grade. Grades 1 to 3 apply only to adenocarcinomas. Grade 4, or undifferentiated carcinoma, is used to describe tumours with cancer cells that are undifferentiated. This means that they don’t look or act like normal cells. Grade 4 is only used for tumours that don’t start in gland cells or make mucus, including neuroendocrine tumours and squamous cell carcinomas.
Knowing the grade gives your healthcare team an idea of how quickly the cancer may be growing. This helps them plan your treatment. The grade can also help the healthcare team predict how you might respond to treatment.
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