PracticeUpdate: Haematology & Oncology

BREAST 26

Annals of Internal Medicine Take-home message Breast cancer screening: tumour size and overdiagnosis EDITOR’S NOTE By Lee S. Schwartzberg MD, FACP S ince mammographic screening for breast cancer began 40 years ago, our knowledge of the disease has

• The authors evaluated the relationship among breast cancer screening, detected tumour size, and overdiagnosis rate using a cohort of Danish patients. Screening was not associated with a lower incidence of advanced tumours; however, the incidence of nonadvanced tumours increased with screening. • The overall rate of over-diagnosis was 48.3% in 2010. Abstract

increased immeasurably. We know now that there are different subgroups of breast cancer with markedly different nat- ural histories. Knowing this has given rise to the concept of overdiagnosis, meaning finding a tumour in a patient that is des- tined to never be life-threatening. Hence, working to diagnose this increases anxiety without providing net health benefit. We still do not know exactly how to predict this on an individual tumour level. Using the Danish staggered experience with the introduction of screening mam- mography and a relatively complete national cancer registry, researchers pub- lishing in Annals of Internal Medicine claim that screening does not reduce the incidence rate of advanced breast tumours. Their definition of advanced tumour is somewhat arguable as it is lim- ited to a size definition of >2 cm without accounting for biologic subtype or posi- tive lymph nodes. The advanced tumour rate did not decrease over time, although DCIS diagnosis rates increased substan- tially. In another analysis, they estimated the over-diagnosis rate to be 24% to 48% of all tumours when considering both invasive and DCIS detection. The use of mammography continues to be controversial because of data like these. Yet, the message to the lay public should continue to emphasise that mammogra- phy, while not a perfect test, saves lives. Clearly, we still have much to learn about the optimal frequency of screening and the best age to start and stop screening from a population perspective. For an individual woman, appropriate use of screening should continue at intervals and ages recommended by her physician.

Screening was not associated with a lower incidence of advanced tumours; however, the incidence of nonadvanced tumours increased with screening.

BACKGROUND Effective breast cancer screening should detect early-stage cancer and prevent advanced disease. OBJECTIVE To assess the association between screening and the size of detected tumors and to estimate overdiagnosis (detection of tum- ors that would not become clinically relevant). DESIGN Cohort study. SETTING Denmark from 1980 to 2010. PARTICIPANTS Women aged 35 to 84 years. INTERVENTION Screening programs offering biennial mammography for women aged 50 to 69 years beginning in different regions at different times. MEASUREMENTS Trends in the incidence of advanced (>20 mm) and nonadvanced (≤20 mm) breast cancer tumors in screened and nonscreened women were measured. Two approaches were used to estimate the amount of overdiagnosis: comparing the incidence of

was not associated with a reduction in the inci- dence of advanced cancer. It is likely that 1 in every 3 invasive tumors and cases of DCIS diagnosed in women offered screening rep- resent overdiagnosis (incidence increase of 48.3%). Breast cancer screening in Denmark: a cohort study of tumor size and overdiagnosis. Ann Intern Med 2017 Jan 10;[EPub Ahead of Print], KJ Jørgensen, PC Gøtzsche, M Kalager, et al.

advance and nonadvanced tum- ors among women aged 50 to 84 years in screening and nonscreen- ing areas; and comparing the incidence for nonadvanced tumors among women aged 35 to 49, 50 to 69, and 70 to 84 years in screening and nonscreening areas. RESULTS Screening was not asso- ciated with lower incidence of advanced tumors. The incidence of nonadvanced tumors increased in the screening versus prescreen- ing periods (incidence rate ratio, 1.49 [95% CI, 1.43 to 1.54]). The first estimation approach found that 271 invasive breast cancer tumors and 179 ductal carcinoma in situ (DCIS) lesions were overdiagnosed in 2010 (overdiagnosis rate of 24.4% [including DCIS] and 14.7% [excluding DCIS]). The second approach, which accounted for regional differences in women younger than the screening age, found that 711 invasive tumors and 180 cases of DCIS were overdi- agnosed in 2010 (overdiagnosis rate of 48.3% [including DCIS] and 38.6% [excluding DCIS]). LIMITATION Regional differences com- plicate interpretation. CONCLUSION Breast cancer screening

Dr Schwartzberg is a senior partner and Medical Director of the West Clinic, a 30-physician practice specialising in oncology, haematology and radiology

located in Memphis, Tennessee.

PRACTICEUPDATE HAEMATOLOGY & ONCOLOGY