Review by urological pathologists improves the accuracy of Gleason grading by general pathologists

Biopsy GS is an important predictor of the likelihood of various final pathological stages of radical retropubic prostatectomy [ 7], and it is also a significant predictor of biochemical recurrence in patients who undergo radical prostatectomy [ 16, 17]. Biopsy GS is also associated with biochemical failure in those who have undergone permanent brachytherapy [ 18] and external beam radiation therapy [ 19]. Biopsy GS, in combination with PSA level and clinical stage, is a very important factor in decision making for initial therapy. However, several studies have described interobserver variability in Gleason grading [ 8, 9]. In particular, the variability in Gleason grading between general pathologists should not be overlooked [ 8, 10]. Burchardt et al. demonstrated that 29 German pathologists who analyzed a series of tissue microarray images showed 45.7 % concordance with biopsy GS assigned by an expert. [ 20] Coard et al. reported 67 % overall concordance between anatomical pathologists and an experienced pathologist for consensus on prostate cancer GS [ 10]. In the present study, the overall concordance between general pathologists and the urological pathologists was 47.5 % and the kappa score was 0.55 in the first 6-month period. This was not an acceptable concordance and was similar to the results of previous studies. These discrepancies may have been caused by (1) a sampling effect caused by tumor heterogeneity, (2) interpretational bias, or (3) the small volume of tissue for cancer biopsy [ 10, 21]. In the present study, patients who diagnosed with prostate cancer on one positive core tended to be misdiagnosed compared to those who diagnosed on two or more cores and another reason for discordance may have been that the general pathologists did not refer to the 2005 ISUP consensus conference on the Gleason grading of Prostatic Carcinoma [ 11].

To improve this discrepancy, Mikami et al [ 22] used a 40-min educational lecture or a tutorial with an anatomical atlas. In a lecture group, the average concordance rates before and after the lecture were 55.7 % and 68.4 %, and the average kappa values were 0.43 and 0.67, respectively. In the atlas group, the average concordance rates before and after providing the atlas were 61.3 % and 74.5 %, and the average kappa values were 0.44 and 0.68, respectively. Allsbrook et al [ 8] reported that concordance between general pathologists and urological pathologists improved to 77.4 % (kappa value = 0.73) by web-based virtual microscopy. In Egevad’s study, the proportion of correct GS improved from 70.5 % to 86.6 % after a teaching set of 40 images illustrating GS was distributed among 85 pathologists [ 23]. The present study demonstrated an improvement in the accuracy of general pathologists’ GS after review by 2 urological pathologist. The rate of agreement and the kappa value increased with the period and improved from an initial 47.5 % (kappa score = 0.55) to a final 80.3 % (kappa value = 0.84). Furthermore in the third period, the rate of concordance was high and the high rate continued in the last period. So the appropriate time of this method for improving GS may need one year by our way.

It is well known that general pathologists tend to underestimate GS [ 8, 10, 20, 24]. Coard et al. reported that anatomical pathologists undergraded 25.6 % of all biopsy specimens and overgraded 6.7 % [ 10], whereas Burchardt et al. reported that the rates of undergrading and overgrading were 38.9 % and 15.4 %, respectively [ 20]. Similar to our reports, Barqawi et al. evaluated defference between outside pathologists and their institution pathologists and Gleason undergrading occurred in 46 % outside and 38 % their institution diagnosis with respect to radical prostatectomy specimens [ 24]. The corresponding values in the first period in the present study were 35.1 % and 18.1 %, respectively, showing that general pathologists tended to undergrade as in other reports. Undergrading was particularly common for tumors with a GS of 6 and 3 + 4 in our study. Allsbrook et al. found 47 % undergrading of tumors with GS 5–6, and 43 % undergrading of tumors with GS 7 [ 8]. In the present study, the undergrading of GS in 7 samples most probably resulted from mistaking Gleason pattern 4 for pattern 3, and the undergrading of GS in 6 tumors most probably resulted from mistaking pattern 3 for pattern 2. This is in accordance with the studies of Allsbrook et al. [ 8], Burchardt et al. [ 20], and Mikami et al. [ 22] Thus, there is a tendency for general pathologists to underestimate GS, especially in Gleason patterns 3 and 4.

However, the rate of undergrading decreased to 16.4 % in the last period after general pathologists had the experienced of review by the urological pathologists in the present study. Mikami et al. reported an improvement in the rate of undergrading from 36.3 % to 14.2 % after a lecture [ 22]. Egevad reported improvement of undergrading by the use of reference images [ 23]. It shows that the tendency for general pathologists to undergrade can improve when they study GS patterns using any of the common methods. Particular improvement in undergrading among general pathologists can be expected by preventing mistakes in identifying Gleason pattern 3 for pattern 2 and pattern 4 for pattern 3.

A limitation of this study was the inability to isolate the general pathologists from other educational sources associated with Gleason scoring over a period of 2 years. Therefore, any improvement seen may not necessarily be a direct result of the experience of the review by the urological pathologists.