Unifocal, multifocal and diffuse carcinomas: a reproducibility study of breast cancer distribution

Multifocality of invasive breast carcinoma has been associated with prognostic disadvantage. Unifocal, multifocal and diffuse distributions have been recently defined for both inasive carcinomas and in situ components, and these have been combined into categories of prognostic relevance. Eight observers analyzed the same series of 30 megaslides from 29 carcinomas, and had to classify the lesions into the three distribution patterns of unifocal, multifocal or diffuse (or not present/non influential). The reproducibility of the distribution patterns of invasive carcinomas was better than that of the in situ carcinoma components, but was still only fair to moderate on the basis of kappa values. The reproducibility of DCIS was poor to slight with some kappa values reflecting agreement by chance only. The results suggest the definitions of these distribution patterns require refinements for a more reliable and reproducible diagnosis if one wants to associate prognostic information with this variable.