Clinicopathological differences between interval and screen-detected breast cancers diagnosed within a screening programme in Northern Portugal

Abstract

Objective To evaluate clinicopathological differences between screen-detected (SD) and interval (IC) breast cancers diagnosed in women enrolled in an organized breast screening programme in 2000--2007. Setting Breast Cancer Screening Programme of the north region of Portugal. Methods Using data from the screening programme and from the population-based North Region Cancer Registry, SD and IC were identified. Information on screening history, age, date of diagnosis, tumour size, histological type and grade, lymph node status, tumour stage, biomarkers, and treatment was obtained from the cancer registry and from clinical and pathological reports. Association between mode of detection and these clinicopathological characteristics was estimated by unconditional logistic regression. Results A total of 442 SD and 112 IC were identified in women aged 50--69. Compared with SD, IC were diagnosed in younger women (60.0 ± 5.8 years and 58.4 ± 6.0 years, respectively), were larger (tumour size >20 mm: 60.2% versus 25.1%), lobular (6.3% versus 16.1%), with a higher differentiation grade (grade 3: 17.7% versus 38.9%), had more lymph node metastases, more advanced stage, and oestrogen receptor (ER) negative (12.9% versus 29.0%) and progesterone negative, and HER2 positive. After multivariable analysis, compared with SD, IC were more likely to be larger than 20 mm, lobular, of grade 3 and negative for ER. Conclusion Our results are consistent with other studies. IC’s have a more aggressive biology than SDs. Our findings did not show any unexpected pattern requiring changes to our screening procedures, but continuous identification and characterization of IC is advisable.