Which pattern is not part of the equation used to determine a Gleason score for prostate cancer?

The Gleason score is a histopathological grading system used to evaluate the aggressiveness of prostate cancer based on the architectural patterns of cancer cells observed in tissue specimens. In this scoring system, two primary patterns are identified: the primary pattern, which is the most prevalent histological pattern seen, and the secondary pattern, which is the second most prevalent.

The tertiary pattern, while it can be noted during evaluation, is not factored into the final Gleason score. Instead, it provides additional context regarding the tumor's variability but does not alter the primary and secondary patterns that drive the score calculation.

Thus, the identification of the tertiary pattern is not part of the formal equation used to derive the Gleason score, which is solely based on the primary and secondary patterns.