Breast Cancer Diagnosed Between Mammograms Isn't More Aggressive

Summary and Comment

Breast Cancer Diagnosed Between Mammograms Isn't More Aggressive

Women with "interval" breast cancers had the same prognosis as women with breast cancers who were never screened.

Are breast cancers diagnosed in women who have had previously normal screening mammograms more aggressive than breast cancers diagnosed in women who haven't undergone screening mammograms? To find out, Norwegian investigators carried out a population-based observational study.

In Norway, older women (age, 50–72) now are invited to receive screening mammography every 2 years. Study participants were 1800 women with "interval breast cancer" (diagnosed within 26 months of their last normal screening mammograms and before their next scheduled mammograms) and 5300 women with breast cancer who had not undergone screening mammography. Compared with the nonscreened group, women in the interval-cancer group exhibited slightly higher percentages of lobular cancers, large tumors (>2 cm), negative lymph nodes, and stage II (vs. stage I) disease. However, breast cancer–related mortality and overall mortality at 10 years were not significantly different between the groups. Notably, in the interval-cancer group, tumor size, node status, grade, and hormone-receptor status were not associated with time since last normal screening mammogram.

Comment: In this study, women with interval breast cancers had the same prognosis as women with breast cancer who had not been screened. The investigators did not compare the prognosis of women with interval breast cancers to the prognosis of women with screen-detected breast cancers, because screen-detected breast cancers are affected by length bias sampling, lead time bias, and overdiagnosis bias. Thus, the comparisons in this study are valid.

— Paul S. Mueller, MD, MPH, FACP

Published in Journal Watch General Medicine January 2, 2013

Citation(s):

Kalager M et al. Prognosis in women with interval breast cancer: Population based observational cohort study. BMJ 2012 Nov 16; 345:e7536. (http://dx.doi.org/10.1136/bmj.e7536)

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