The pathologic diagnosis of
adrenocortical carcinoma (ACC) still needs to be improved, because the renowned Weiss Score (WS) system has a poor reproducibility of some parameters and is difficult to apply in borderline cases and in ACC variants. The "
reticulin algorithm" (RA) defines
malignancy through an altered
reticulin framework associated with 1 of the 3 following parameter:
necrosis, high mitotic rate, and vascular invasion. This study aimed at validating the interobserver reproducibility of
reticulin stain evaluation in an unpublished series of 245 adrenocortical
tumors (61
adenomas and 184
carcinomas) from 5 Italian centers, classified according to the WS. Eight pathologists reviewed all
reticulin-stained slides. After training, a second round of evaluation on discordant cases was performed 10 weeks later. The RA reclassified 67 cases (27%) as
adenomas, including 44 with no
reticulin alterations and 23 with an altered
reticulin framework but lacking the subsequent parameters of the triad. The other 178 cases (73%) were
carcinomas according to the above-mentioned criteria. A complete (8/8 pathologists) interobserver agreement was reached in 75% of cases (κ=0.702), irrespective of case derivation, pathologists' experience, and histologic variants, and was further improved when only those cases with high WS and clinically malignant behavior were considered. After the training, the overall agreement increased to 86%. We conclude that
reticulin staining is a reliable technique and an easy-to-interpret system in adrenocortical
tumors; moreover, it has a high interobserver reproducibility, which supports the notion of using such a method in the proposed 2-step RA approach for ACC diagnosis.