Histopathologic classification of breast cancer in Sweden and Italy: a comparison between two pathologists

Two large series of breast cancers (BC), identified in the Pathology Departments of Malmö (Sweden) and Florence (Italy), were independently reviewed by two experienced pathologists, one from each department. Overall, comparison of diagnoses of 372 BCs according to a simplified WHO histologic classification system (in four combined categories) revealed agreement for 74% of the cases. Concordance, as measured by the kappa statistic, was relatively good (0.53 overall). Kappa values for specific categories were also acceptable, being highest for "invasive lobular" BC (0.63) and lowest for "other types" (0.45). The kappa value for "noninvasive" versus all other categories of invasive BC was 0.53. Some BCs were systematically classified as "noninvasive" by one pathologist and as "invasive ductal with a predominant intraductal component" by the other. Invasive lobular BCs were also diagnosed more frequently by one pathologist. These findings suggest that when planning geographical or temporal comparisons of distribution for BC histologic categories, standardization of classification and a centralized review may play an important role.