Tumour characteristics of screen-detected and interval cancers in the Flemish Breast Cancer Screening Programme: A mammographic breast density study

Objective: The objective is to investigate tumour prognostic factors versus breast density in screen-detected cancers and interval cancers. The results may highlight the need for more personalised screening protocols based on breast density in organized screening programmes.

Study design: A retrospective study was performed of tumour characteristics of screen-detected cancers (n=468) and interval cancers (n=515) of 983 women who participated in the Flemish Breast Cancer Screening Programme in 2009-2010. Breast density was obtained from the screening programme data. Information on nodal invasion and histological grading was taken from the Belgian Cancer Registry. Tumour size and proliferation and receptor expression status were retrieved from pathology reports. The differences in tumour characteristics between screen-detected and interval cancers as well as the variation in these variables with breast density in both groups were studied by logistic regression.

Results: A comparison of tumour characteristics between screen-detected cancers and interval cancers systematically showed features of more aggressive tumours in interval cancers: larger tumour size, nodal invasion, grade 3 tumours, and hormone receptor negative phenotype (p<0.05). The analysis of tumour characteristics versus breast density in screen-detected cancers showed higher numbers of aggressive grade 3 tumours in low-density breasts and of the luminal A subtype with good prognosis in high-density breasts (p<0.05). This analysis for interval cancers highlights a high proportion of the difficult-to-treat triple-negative subtype in low-density breasts compared with high-density breasts. In conclusion, the study data support arguments against changes in breast cancer screening programmes with prolongation of screening intervals in low-density breasts.