Differences between cancers detected in prophylactic mastectomy specimen, screen detected cancers and true interval cancers in women participating in an intermediate and high risk screening program

S. Vreemann, A. Gubern-Mérida, S. Lardenoije, N. Karssemeijer and R. Mann

European Breast Cancer Conference 2016.

Background: Intensive screening with annual mammography and MRI is offered to women at high risk for the development of breast cancer. Although most cancers are screen detected, screening does not prevent breast cancers from occurring and some are still detected between screening rounds (true interval cancers). Consequently, some women opt for prophylactic mastectomy rather than intensive screening since this reduces the incidence of breast cancer. Unfortunately, detection of cancer in a prophylactic mastectomy specimen (incident cancers) is not a rare occurrence. It is unsure whether these cancers should be considered as interval cancers. This study evaluates the prognostic factors of cancers stratified by the mode of tumor detection in these women.

Material and methods: Review of our intermediate and high risk screening program from 2003 to 2013 identified 177 cancers. Of these, 136 were detected in screening, 15 cancers were true interval carcinomas detected due to symptoms, and 26 cancers were detected in prophylactic mastectomy specimens. Patient- and cancer characteristics (invasive versus in-situ disease, grade, pT-stage, age, menopausal state, cancer receptor status and pN-stage) between these three groups were compared using a Pearson's chi-square test for categorical variables or one-way ANOVA for continuous variables.

Results: The fraction of invasive disease was 8/26 (30.8%), 109/136 (80.1%) and 15/15 (100%) for cancers in prophylactic mastectomy specimens, screen detected cancers and interval cancers, respectively (p<0.001). The fraction of cancers larger than two centimeters was 1/26 (3.8%), 24/136 (17.6%) and 3/15 (20.0%), respectively. A similar increase was observed for the overall pT-stage (p<0.001). Moreover, tumor grade was higher in true interval cancers than in cancers detected in prophylactic mastectomy specimens (p=0.001). Most cancers were node negative (p=0.233). There were no significant differences in patient age, menopausal state, cancer receptor status, and pN-stage between true interval cancers and prophylactic mastectomy specimens.

Conclusions: True interval cancers are more often invasive, generally larger, and commonly of higher grade than screen detected cancers or cancers in prophylactic mastectomy specimens. The prognosis of cancers detected in prophylactic mastectomy specimens is particularly good as most of these lesions are in situ cancers only. Therefore, these incident cancers should not be regarded as interval cancers.