Introduction to Clinical Oncology
Cancer Grading

Cancer Grading


Grading is based on the review of tissue by a pathologist and has to do with how the cancer cells look and thus about how they are expected to grow and spread.

Like staging, tumour grade is important when making decisions about treatment and when talking with patients about prognosis and the expected course of disease.


Grading considers:

  • structure

  • growth

  • pattern of cells

Histological grade or differentiation is about how closely the tumour cells resemble the cells from which they originated. Well-differentiated tumours are considered to be prognostically more favourable than undifferentiated.


Nuclear grade refers to the size and shape of the nucleus in tumour cells and the percentage of tumour cells dividing - those with a low nuclear grade grow and spread less quickly than cancers with high nuclear grade.


There are different grading systems for each type of cancer.

For example, pathologists use the Gleason system to describe the degree of differentiation of prostate cancer cells. The Gleason system uses scores ranging from Grade 2 to Grade 10. Lower Gleason scores describe well-differentiated, less aggressive tumors. Higher scores describe poorly differentiated, more aggressive tumors.


Bowel cancer scenario

Excluding non-melanomatous skin cancer, colorectal cancer is the third leading cause of cancer among North Americans. There is an orderly pathway of tumorogenesis and progression from mucosal hyperplasia to polyp to invasive cancer is well documented. Tumors are graded based on histopathological assessment: well, moderately and poorly diffentiated cancers being graded 1, 2 or3, respectively. Cancers are staged as per the TNM staging system.


Mr. AK is a 64 yo business man from Napanee who presented with microcytic anemia and change in bowel habit. Colonoscopy revealed a tumor in the rectum. Biopsy confirms a moderately differentiated cancer. A transrectal ultrasound suggests the lesion is invading the perirectal fat and the presence of 2 enlarged lymph nodes. A CXR and liver ultrasound fail to identify metastatic disease.

What is the pre-operative grade and stage?


He has an anterior resection and the pathology identifies well differentiated cancer that invades the muscularis propria, but not the pericolic fat. None of 20 resected lymph nodes were involved.