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Objectives: Biological markers that predict the development of invasive breast cancer are needed to improve personalized therapy for patients diagnosed with ductal carcinoma in situ. We investigated the role of basal cytokeratin 5/6 in the risk of invasion in breast ductal carcinoma in situ., Methods: We constructed tissue microarrays using 236 ductal carcinoma in situ samples: 90 pure samples (group 1) and 146 samples associated with invasive carcinoma (group 2). Both groups had similar nuclear grades and were obtained from patients of similar ages. The groups were compared in terms of estrogen (ER) and progesterone receptor (PR) status, human epidermal growth factor receptor 2 (HER2) expression, cytokeratin 5/6 immunostaining, human epidermal growth factor receptor 1 (EGFR) membrane staining and molecular subtype, as indicated by their immunohistochemistry profiles., Results: ER/PR-negative status was predictive of invasion, whereas HER2 superexpression and cytokeratin 5/6-positive status were negatively associated with invasion. Among the high-grade ductal carcinoma in situ cases, a triple-positive profile (positive for estrogen receptor, progesterone receptor, and HER2) and cytokeratin 5/6 expression by neoplastic cells were negatively associated with invasion. In the low-grade ductal carcinoma in situ subgroup, only cytokeratin 5/6 expression exhibited a negative association with the probability of invasion., Conclusion: The immunohistochemical expression of cytokeratin 5/6 by ductal carcinoma in situ epithelial cells may provide clinically useful information regarding the risk of progression to invasive disease.

Purpose: To compare the prognostic and predictive features between in situ and invasive components of ductal breast carcinomas., Methods: We selected 146 consecutive breast samples with ductal carcinoma in situ (DCIS) associated with adjacent invasive breast carcinoma (IBC). We evaluated nuclear grade and immunohistochemical expression of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), cytokeratin 5/6 (CK5/6), and epidermal growth factor receptor (EGFR) in both components, in situ and invasive, and the Ki-67 percentage of cells in the invasive part. The DCIS and IBC were classified in molecular surrogate types determined by the immunohistochemical profile as luminal (RE/PR-positive/ HER2-negative), triple-positive (RE/RP/HER2-positive), HER2-enriched (ER/PR-negative/HER2-positive), and triple-negative (RE/RP/HER2-negative). Discrimination between luminal A and luminal B was not performed due to statistical purposes. Correlations between the categories in the two groups were made using the Spearman correlation method., Results: There was a significant correlation between nuclear grade (p<0.0001), expression of RE/RP (p<0.0001), overexpression of HER2 (p<0.0001), expression of EGFR (p<0.0001), and molecular profile (p<0.0001) between components in situ and IBC. CK 5/6 showed different distribution in DCIS and IBC, presenting a significant association with the triple-negative phenotype in IBC, but a negative association among DCIS., Conclusions: Our results suggest that classical prognostic and predictive features of IBC are already determined in the preinvasive stage of the disease. However the role of CK5/6 in invasive carcinoma may be different from the precursor lesions.