How is the Gleason score determined?

• A. From the most common pattern only
• B. From the two most common histologic patterns, each graded 1–5, then summed.
• C. From tumor size
• D. From PSA level

Answer: (B)

The Gleason score is based on how the cancer tissue looks under the microscope, specifically its glandular architecture, not on how big the tumor is or what the PSA level is. The pathologist identifies the two most common architectural patterns seen in the tumor and assigns each a grade from 1 to 5 (1 = most like normal glands, 5 = very abnormal with little gland formation). These two grades are then added together to give the Gleason score. The first number is the primary pattern (the most common one) and the second is the secondary pattern (the next most common). For example, a tumor with pattern 3 as the most common and pattern 4 as the next most common would have a Gleason score of 3+4 = 7. This method captures the tumor’s heterogeneity and is why the correct option emphasizes two patterns summed to yield the score.