The abnormality of cancer, when viewed under the microscope, is what the grade of the cancer is based upon. Cancer with higher grades are more likely to grow at a faster rate and they also are more abnormal to look at. There are basically two main ways by which the grade of prostate cancer is measured:
The Gleason system assigns grades based on the severity of prostate cancer. Grade 1 is assigned to cancer that looks a lot like the normal prostate tissue. In case the cancer cell looks very abnormal, it is then assigned grade 5. Grades 2 to 4 fall in between these extremes. However most of the times all cancers fall between the grades of 3 to 5, grades 1 and 2 are rarely used.
A grade is assigned to the two areas that make up most of cancer, as prostate cancer often have areas that belong to different grades. The sum of these two grades is calculated to form the Gleason Score. The grade that is most common in the tumor is allotted the first grade. To give an example, let’s assume that most of the tumor falls under grade 3 and less of the tumor is assigned to grade 4, then the Gleason Score is written as 3+4=7. Hence the Gleason Score, in this case, will be 7. There are also some exceptions when cancer has three grades. In such cases, the Gleason Score is modified in order to reflect the aggressive nature of cancer. Although, theoretically the Gleason Score can range anywhere between grades 2 to 10, scores below 6 are rarely used.
Based on the Gleason Score, prostate cancers are often dived into three groups:
- Low grade or well-differentiated: These are cancers that have a Gleason Score of 6 or less.
- Intermediate Grade or moderately-differentiated: This group housed cancers that have a Gleason Score of 7.
- High Grade or poorly-differentiated: Cancers with the Gleason Scores of 8 to 10 fall in this category.
Doctors have recently come to realize the truth that prostate cancer can actually be divided into more than three groups. It has been found that men with Gleason Score 3+4=7 cancer tend to do better than men with 4+3=7 cancer. Similarly, men with a Gleason Score 8 cancer tend to do better than those with a Gleason Score of 9 to 10. Hence, doctors have developed Grade Groups ranging from 1 to 5 – Grade Group 1 = Gleason Score 6 (or less); Grade Group 2 = Gleason Score 3+4=7; Grade Group 3 = Gleason Score 4+3=7; Grade Group 4 = Gleason Score 8; Grade Group 5 = Gleason Score 9-10. Over time the Grade Group will likely replace the Gleason Score. But for now, you might see either one or sometimes both on a biopsy pathology report.