Context Selection of systemic adjuvant therapies for women diagnosed as having
breast cancer is based on risk estimations for cancer recurrence. In such
estimations, tumors detected by mammography screening are considered to be
associated with a similar risk of recurrence as tumors of similar size found
by other methods.
Objective To compare the risk of recurrence and survival among women with cancerous
tumors detected by mammography screening compared with other methods (outside
Design, Setting, and Patients Retrospective study comparing clinical, histopathological, and biological
features of cancerous tumors detected by mammography screening compared with
tumors detected outside of screening. Women diagnosed as having breast cancer
in 1991 or 1992 were identified from the Finnish Cancer Registry (n = 2842).
The median follow-up time was 9.5 years. Cancer biological variables were
analyzed from tumor tissue microarrays using immunohistochemistry or in situ
hybridization and included ERBB2, TP53, and MK167 expression and ERBB2 amplification data.
Main Outcome Measures Univariate and multivariate analyses of potential risk factors for distant
recurrence of breast cancer and 10-year survival.
Results Of the 1983 women with unilateral invasive breast cancer, data on tumor
diameter were available for 1918 women. Women with cancerous tumors detected
by mammography screening had better estimated 10-year distant disease-free
survival than women with tumors found outside of screening (tumor size of
≤10 mm [n = 386] 92% vs 85% [P = .04]; 11-20 mm
[n = 808] 88% vs 76% [P<.001]; 21-30 mm [n = 409]
86% vs 63% [P = .008]; >30 mm [n = 315] 68% vs 50%
[P = .12], respectively). In a Cox multivariate model
that included cancer biological factors, the relative hazard ratio for distant
recurrence among women with tumors detected outside of screening (HR, 1.90;
95% confidence interval, 1.15-3.11) was significantly higher than among women
with tumors detected by mammography screening (P =
.01). Breast cancer diagnosis by mammography screening was an independent
prognostic variable reducing the relative HR for distant recurrence. This
effect was equal to or greater than the effect of 1-cm decrease in tumor diameter
(HR, 1.20; 95% confidence interval, 1.10-1.31).
Conclusions Cancerous tumors detected by mammography screening are associated with
a better prognosis than tumors of similar size found outside of screening.
The risk of distant metastases is overestimated for women diagnosed as having
cancer by mammography screening unless the method of detection is taken into
account in risk estimations.