Biological characteristics of interval cancers: a role for biomarkers in the breast cancer screening.

INTRODUCTION: In a population-based screening program, a percentage of tumors remain undetected; these tumors comprise a heterogeneous group, and they are more likely to have adverse prognostic features. The aim of this study was to identify differences in biological characteristics of screen-detected versus interval breast cancers in a population-based screening program according to molecular subtypes. MATERIALS AND METHODS: We analyzed the population-based data from a long-running screening program in the area of Florence. Data on screening history and on age, T and N status, grade, histotype, hormonal status and Ki-67 and HER2 expression were retrieved. Subtypes of breast cancer were defined on the expression of ER, PR, Ki-67 and HER2: luminal A if ER/PR+, HER2- and Ki67 <14 %, luminal B (HER2 negative) if ER/PR+, HER2- and Ki67 ≥14 %, luminal B (HER2 positive) if ER/PR+ and HER2+, triple negative if ER/PR-and HER2-, HER2 positive if ER/PR- and HER2+. Association between molecular subtypes and mode of detection will be evaluated by a logistic regression model adjusted for the potential confounding variables. RESULTS: Information about biomarkers was known for 277 cases, 211 screening-detected and 66 interval cancers. Among interval cases, the triple-negative cancers were more represented than luminal A (OR = 3.52; CI, 1.112-11.13; p = 0.0319), while the proportion of HER2+ was quite similar (OR = 1.57; p = 0.4709). CONCLUSION: Although made on a small number of cases, our results suggest a difference in distribution of molecular subtypes according to mode detection, confirming the results of earlier studies.