Effect of mammography screening on mortality by histological grade
Menée à partir des données d'un essai suédois portant sur 77 080 femmes invitées à participer à un programme de dépistage du cancer du sein par mammographie (âge : 40 à 74 ans) et à partir de données portant sur 55 985 témoins, cette étude évalue l'effet du programme de dépistage sur la mortalité par cancer du sein et sur le grade histologique de la tumeur au diagnostic
Background : It has been asserted that mammography screening preferentially benefits those with less aggressive cancers, with lesser or no impact on more rapidly progressing and therefore more life-threatening tumours.
Methods : We utilized data from the Swedish Two-County Trial, which randomized 77,080 women aged 40-74 to invitation to screening and 55,985 for usual care. We tabulated cancers by histological grade and then compared mortality from cancers specific to histological grade between the invited and control group using Poisson regression, with specific interest in the effect on mortality from grade 3 cancers. We used incidence-based mortality from tumours diagnosed within the screening phase of the trial. Finally, we cross-tabulated grade with tumour size and node status, to assess downstaging within tumour grades.
Results : There was a major reduction in mortality from grade 3 tumours (RR = 0.65, 95% CI 0.53-0.80, p<0.001), and more deaths prevented from grade 3 tumours (N=95) than grade 1 and 2 tumours combined (N=48) in the invited group. The proportions of tumours ≥15 mm or larger and node positive tumours were substantially reduced in the grade 3 tumours in the invited group.
Conclusions : The combination of prevention of tumours progressing to grade 3 and detection at smaller sizes and lesser rates of lymph node metastases within grade 3 tumours results in a substantial number of deaths from grade 3 cancers being prevented by invitation to mammographic screening.
Impact : Mammography screening prevents deaths from aggressive cancers.
Cancer Epidemiology Biomarkers & Prevention , article en libre accès, 2016