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. 2020 Oct;111(5):787-793.
doi: 10.17269/s41997-020-00305-6. Epub 2020 Mar 6.

The incidence of breast cancer in Canada 1971-2015: trends in screening-eligible and young-onset age groups

Emily Heer  1 , Yibing Ruan  1 , Nicole Mealey  2 , May Lynn Quan  2   3   4 , Darren R Brenner  5   6   7
Affiliations

The incidence of breast cancer in Canada 1971-2015: trends in screening-eligible and young-onset age groups

Emily Heer et al. Can J Public Health. 2020 Oct.

Abstract
in English, French

Objectives: Breast cancer incidence has fluctuated considerably in Canada, with recent reductions in rates among screening-eligible women. However, incidence of early-onset and pre-menopausal breast cancer is understudied. We examined age-specific trends in breast cancer incidence between 1971 and 2015, as well as possible trends by birth cohort.

Methods: Incidence data were collected from the National Cancer Incidence Reporting System and the Canadian Cancer Registry, and annual percent changes were estimated using the Joinpoint Regression Program. Five-year birth cohort models were fit using the National Cancer Institute's web tool.

Results: Breast cancer incidence among women under age 40 has increased since 2000, while incidence under 50 has remained stable. Rates of post-menopausal breast cancer declined sharply and have recently plateaued. More recent birth cohorts are at a non-significantly increased risk of breast cancer compared with the reference, with an increasing upward trend.

Conclusions: Rates of breast cancer may be increasing among younger women, and there is suggestive evidence that more recent birth cohorts are at increased risk of the disease. More research is needed into the risk factors for pre-menopausal breast cancer to support primary prevention efforts in this area.

Objectifs: L’incidence du cancer du sein fluctue considérablement au Canada, avec des baisses récentes des taux chez les femmes admissibles au dépistage. Par contre, l’incidence du cancer du sein à début précoce et préménopausique est insuffisamment étudiée. Nous avons examiné les tendances selon l’âge de l’incidence du cancer du sein entre 1971 et 2015, ainsi que les éventuelles tendances par cohorte de naissance.

Méthode: Les données sur l’incidence proviennent du Système national de déclaration des cas de cancer et du Registre canadien du cancer, et les pourcentages de changement annuel ont été estimés à l’aide du programme de régression Joinpoint. Des modèles de cohorte de naissance de 5 ans ont été adaptés à l’aide d’un outil en ligne de l’Institut national du cancer.

Résultats: L’incidence du cancer du sein chez les femmes de moins de 40 ans augmente depuis 2000, tandis qu’elle est stable chez les femmes de moins de 50 ans. Après avoir diminué abruptement, les taux de cancer du sein postménopausique ont plafonné récemment. Les cohortes de naissance plus récentes présentent un risque accru non significatif de cancer du sein comparativement aux cohortes de référence, avec un mouvement de hausse.

Conclusions: Les taux de cancer du sein peuvent sembler croître chez les jeunes femmes, et les données portent à croire que les cohortes de naissance plus récentes présentent un risque accru pour cette maladie. Il faudrait pousser la recherche sur les facteurs de risque de cancer du sein préménopausique pour appuyer les démarches de prévention primaire dans ce domaine.

Keywords: Age of onset; Breast neoplasms; Canada; Incidence; Pre-menopause.

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Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
Breast cancer incidence in Canada among women under the age of 50 from 1971 to 2015. Average annual percent change given in legend. Final selected model includes 0 joinpoints
Fig. 2
Fig. 2
Breast cancer incidence in Canada among women under the age of 40 from 1971 to 2015. Average annual percent changes given in legend. Final selected model includes one joinpoint. ^ indicates that the APC is significantly different from zero at the alpha = 0.05 level
Fig. 3
Fig. 3
Breast cancer incidence in Canada among women age 50–74 from 1971 to 2015. Average annual percent changes (APC) given in legend. Final selected model includes 3 joinpoints. Shaded area represents the period of organized mammography implementation in Canada. The first screening program began in 1988 and the final program in 2004. ^ indicates that the APC is significantly different from zero at the alpha = 0.05 level
Fig. 4
Fig. 4
Rate ratio of breast cancer in Canada by birth cohort. Cohorts from 1888 to 1988, with 1936 as the reference cohort. Shaded area represents 95% confidence intervals
See this image and copyright information in PMC

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