Efficacy of breast cancer screening by age. New results swedish two-county trial

Abstract

Background. Several studies have found a smaller effect of breast cancer screening on breast cancer mortality in women aged younger than 50 years compared with older women. Various possible reasons have been suggested for this, but none firmly is established. Methods. The Swedish Two‐County Study is a randomized trial of breast cancer screening of women aged 40‐74 years, comprising with 133,065 women with a 13‐year follow‐up of 2467 cancers. The Breast Cancer Detection Demonstration Project (BCDDP) is a nonrandomized screening program in the United States, with a 14‐year follow‐up of 3778 cancers in women aged 40‐74 years. The Swedish results by age were updated. The lesser effect of screening at ages 40‐49 years was investigated in terms of sojourn time (the duration of the preclinical but detectable phase) size, lymph node status, and histologic type of the tumors diagnosed in the Swedish Study and their subsequent effect on survival using survival data from both studies. Results. In the Swedish Trial, a 30% reduction in mortality associated with the invitation to screening of women aged 40‐74 years was maintained after 13‐years of follow‐up. The reduction was 34% for women aged 50‐74 years and 13% for women aged 40‐49 years. Results indicated that the reduced effect on mortality for women aged 40‐49 years was due to a differential effect of screening on the prognostic factors of tumor size, lymph node status, and histologic type. The mean sojourn times in the age groups 40‐49 years, 50‐59 years, 60‐69 years, and 70‐74 years were 1.7,3.3,3.8, and 2.6 years, respectively. Conclusions. These results suggest that much, a though not all, of the smaller effect of screening on mo tality in women aged 40‐49 years is due to faster progression of a substantial proportion of tumors in this age group and the rapid increase in incidence during this decade of life. It is concluded that the interval between screenings should be shortened to achieve a greater benefit in this age group. It is estimated that a 19% reduction in mortality would result from an annual screening regime.

Randomised controlled trial of mammographic screening in women from age 40: predicted mortality based on surrogate outcome measures

“…A number of other potential problems with the use of surrogate end points have been discussed by Morrison (1991), such as variation of prognostic factors within measurement categories, most of which would tend to lead to an underestimate of the effect of screening. The analysis of the Swedish Two County Study found that the predicted effect on mortality in the age group 40 -49 years was conservative compared with that observed (Tabar et al, 1995b). The authors hypothesised that this might be attributable to an observed excess of cancers in the intervention arm, possibly due to over diagnosis in this age group, or the existence of a subgroup of women with a long sojourn time.…”

“…The Swedish Two-County Studies Survival index uses information on size, lymph node status, grade and histological type, and has been developed using data from the randomised trial (Tabar et al, 1995b). The relative hazards of different factors, including lymph node status, have previously been validated against observed mortality reduction in the trial in different age-groups including women aged 40 -49 (Tabar et al, 1995a).…”

Comparison of 1- and 2-year screening intervals for women undergoing screening mammography

“…(1) Prognostic model: A Cox proportional hazards model was developed to predict breast cancer-specific survival based on methods published by Tabar et al (1995) and Haybittle et al (1982), using the 'prognostic sample' described above. Age,tumour size (p9,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]50 þ mm,unknown), nodal status (negative, positive, unknown) and histologic grade (well, moderately, or poorly differentiated and unknown) were examined as potential prognostic factors.…”

Performance of clinical mammography: A nationwide study from Denmark

“…Clinical mammography worked significantly better in women above the age of 70 than in women below the age of 50, which is to be expected because of the more favourable differences in contrast on mammography between cancer and the surrounding fatty tissue predominantly seen in elderly age groups. 38 As organized mammography screening was offered in only 2 out of 15 regions in Denmark in 2000 to women aged 50-69, and as the spectrum of accepted reasons for referral to clinical mammography was relatively broad, these examinations may to some extent also have been used for opportunistic screening. We used annual utilisation rate in the region as an indicator of the extent to which the examinations of truly symptomatic women had been mixed with Values in parentheses represent 95% confidence interval.…”