Histopathology of prostate cancer and pathologic staging

The Gleason grading system is the most widely accepted grading system for prostate cancer.1 The Gleason system is based on the glandular pattern of the tumor as identified at relatively low magnification (Figure 11.1). Cytologic features play no role in grading the tumor. Both the primary (predominant) and the secondary (second most prevalent) architectural patterns are identified and assigned a grade from 1 to 5, with 1 the most differentiated and 5 the least differentiated. When Gleason compared his grading system with survival rates, it was noted that in tumors with two distinct tumor patterns the observed number of deaths generally fell in between the number expected on the basis of the primary pattern and that based on the secondary pattern. Since both the primary and secondary patterns were influential in predicting prognosis, there resulted a Gleason score obtained by the addition of the primary and secondary grade patterns. If a tumor had only one histologic pattern, then for uniformity the primary and secondary patterns were given the same grade. Gleason scores range from 2 (1 + 1), which represents tumors uniformly composed of Gleason pattern 1 tumor, to 10 (5 + 5), which represents totally undifferentiated tumors. Gleason pattern 1 and pattern 2 tumors are composed of relatively circumscribed nodules of uniform, single, separate, closely packed, uniform medium-sized glands. Gleason pattern 3 tumor infiltrates in and amongst the non-neoplastic prostate, and the glands have marked variation in size and shape with smaller glands than seen in Gleason patterns 1 or 2. Gleason pattern 4 glands are no longer single and separate as seen in patterns 1 to 3. In Gleason pattern 4, one may also see large irregular cribriform glands as opposed to the smoothly circumscribed smaller nodules of cribriform Gleason pattern 3. Gleason pattern 5 tumor shows no glandular differentiation, composed of either solid sheets, cords, single cells, or solid nests of tumor with central comedonecrosis. Synonyms for Gleason score are “combined Gleason grade” and “Gleason sum.”.