OBSERVER VARIABILITY IN HISTOLOGICAL MALIGNANCY GRADING OF ADENOID CYSTIC CARCINOMAS

The value of malignancy grading of adenoid cystic carcinomas (ACC) is controversial. Some studies have shown that rumours with a solid growt h component have a rapid fatal course, compared to tumours without a s olid growth component. in which recurrences develop even many years af ter initial treatment. Other studies have failed to correlate growth p atterns with clinical course. No universally accepted grading system e xists and no reproducibility studies of the existing grading systems h ave been performed. The aim of this study was to examine the reproduci bility of grading based on semiquantitative assessment of the solid gr owth pattern in ACC. Two different grading systems were assessed by 3 observers on a material of 59 ACC. Interobserver agreement was evaluat ed using the kappa statistic. The reproducibility of grading was poor, except for the category ''solid component constituting 50% or more of the tumour'' (kappa=0.52). It is concluded that quantitative methods are necessary if grading is to be used in prognostic evaluation of ACC . The rarity of the tumours, however, combined with difficulties in di agnosis will impede such investigations unless multicentre studies are undertaken.