Impact of immunohistochemical markers, CK5/6 and E‐cadherin on diagnostic agreement in non‐invasive proliferative breast lesions

Aims:  To assess the impact of cytokeratin (CK) 5/6 and E-cadherin immunohistochemistry on diagnostic agreement of non-invasive proliferative breast lesions. Methods and results:  Twenty pathologists classified 105 cases of non-invasive proliferative breast lesions into 10 diagnostic categories. One haematoxylin and eosin (H&E) slide of each case was analysed on a first round and one H&E slide with corresponding CK5/6 and E-cadherin immunohistochemistry was analysed on a second round. Interobserver reproducibility for category-specific and management-specific lesions was measured on each round. CK5/6 and E-cadherin had little impact on diagnostic agreement, which remained moderate between the first and second rounds (overall κ coefficients of 0.47 and 0.53, respectively, P = NS). Levels of agreement slightly improved for lesions with specific CK5/6 and E-cadherin immunoprofiles (usual ductal hyperplasia, atypical ductal hyperplasia, atypical lobular hyperplasia, lobular carcinoma in situ, non-high-grade ductal carcinoma in situ), but the differences observed were not statistically significant. However, diagnostic agreement improved when lesions were grouped according to their management category (overall κ coefficients of 0.58 and 0.66 in the first and second rounds, respectively). Conclusions:  CK5/6 and E-cadherin immunohistochemistry has little impact on interobserver reproducibility for non-invasive breast lesions. Diagnostic agreement can, however, be improved by grouping lesions in management categories.