Gleason grading system
A pathological grading system used for prostate cancer. It depends on skilled interpretation of the microscopic patterns formed by the cancer which may vary from one area of cancer to the next. The system is widely used, has been extensively studied and appears to be valid for prognosis. The grade of tumour should be distinguished from its stage, which is by a TNM system.
Like many grading systems, it has been modified during development and subsequently in response to changing clinical practice. The most recent modifications were based on a 2005 International Society of Urological Pathology consensus meeting. One salient difference is the the re-classification of cribiform glands from pattern 3 to pattern 4. The use of patterns 1 and 2 in needle biopsies were also deprecated as it was felt that it is rarely possible to confidently call a growth circumscribed when only a minute proportion is available for examination.
While the system can be used reliably on large resection specimens, there is less agreement on how to apply the grading system to needle core biopsies. Although transrectal ultrasound-guided (TRUS) 'sextant' biopsies give 6 cores per side, it still represents only about 1-2% of an average 40cc prostate. It is impossible to know how representative a single core is and there is a dilemma over how to manage small foci of higher grade tumour—does it represent the edge of a larger lesion or a negligibly small area of high grade tumour?
Whereas most cancer grading is based on the worst-looking areas, no matter how infrequent, Gleason scoring is based on the predominant patterns. The score itself is therefore described by the most common pattern (primary grade) followed by the next most frequent pattern (secondary grade), e.g. 3+4. Where only one pattern predominates, the pattern is doubled, i.e. 3+3. Some centres will also denote the third most common pattern, i.e. 3+4 (5 tertiary).
A judgement of the predominant type is easy to make in radical prostatectomy specimens, but less so in core biopsies, where, as mentioned, it is difficult to know how representative each core is.
There is scope for much confusion ("Gleason 4 tumour" could mean 2+2 or 4+4) and, although tedious, it is good practice to be explicit in notation by including the component grades, i.e. Gleason score 7 (4+3), which has the added advantage of distinguishing between 4+3 and 3+4.
The Original 5 Grades
5 categories or grades were described based on increasingly disordered architecture. On a historical/pedantic note, although the terms 'pattern' and 'grades' are commonly used interchangeably, in his original work, Gleason described 9 patterns that were then grouped into the five grades based on outcomes.
The first 2 are rare entities, with grade 1 and 2 occuring as the primary grade in only 0.5% and 1.8% of the original specimens. It appears even less frequently in more contemporary series. The rarity of the entity and the excellent prognosis of these lesions casts doubt over the genuine malignant nature of these patterns as they can closely resemble benign adenosis/atypical adenomatous hyperplasia. With easy access to immunohistochemistry, the diagnosis of patterns 1 and 2 have become exceedingly rare in contemporary series.
- Johns Hopkins university site to improve pathologists' knowledge of, and facility with, Gleason grading.
- ↑ Epstein JI, Allsbrook WC, Amin MB, Egevad LL. The 2005 International Society of Urological Pathology (ISUP) Consensus Conference on Gleason Grading of Prostatic Carcinoma. The American journal of surgical pathology. 2005 Sep; 29(9):1228-42.
- ↑ Hodge KK, McNeal JE, Terris MK, Stamey TA. Random systematic versus directed ultrasound guided transrectal core biopsies of the prostate. The Journal of urology. 1989 Jul; 142(1):71-4; discussion 74-5.
- ↑ Calculation of volume sampled by TRUS core biopsies.
- ↑ Berney DM. Low Gleason score prostatic adenocarcinomas are no longer viable entities. Histopathology. 2007 May; 50(6):683-90.(Link to article – subscription may be required.)
- ↑ Gleason DF. Classification of prostatic carcinomas. Cancer chemotherapy reports. Part 1. 1966 Mar; 50(3):125-8.
- ↑ Gleason DF, Mellinger GT. Prediction of prognosis for prostatic adenocarcinoma by combined histological grading and clinical staging. The Journal of urology. 1974 Jan; 111(1):58-64.
- ↑ Humphrey PA. Gleason grading and prognostic factors in carcinoma of the prostate. Modern Pathology 2004;17:292-306. (Direct link – subscription may be required.)