Study finds women with DCIS diagnosed outside NHS screening face fourfold increase in breast cancer mortality

By Pooja Toshniwal PahariaReviewed by Danielle Ellis, B.Sc.Jan 29 2024

In a recent study published in BMJ, researchers compared the risks of aggressive breast cancers and mortality following ductal carcinoma in situ (DCIS) undetected during screening in the general public to those identified through the National Health Service (NHS) breast screening program.

Background

DCIS, an uncommon disorder, is frequently detected as part of the NHS breast screening program; however, it can also arise outside of it, particularly in women of screening age and older and younger women. Screen-detected DCIS rates are more than twice those in the general population. Understanding the hazards associated with screen-undetected DCIS risks may help evaluate the condition's natural course and potential overtreatment problems.

About the study

In the present study, researchers examined the National Disease Registration Service data to establish the long-term effects of DCIS ascertained outside of the National Health Service breast cancer screening program.

The study examined data from the National Disease Registration Service on 82,009 women between 1990 and 2018 to assess the risks of invasive breast cancers and mortality in women aged 50 to 64 who had non-screen-identified DCIS. The study lasted six months, from the diagnosis of DCIS until the earliest diagnosis, loss of follow-up, the woman's 90th birthday, or December 31, 2018.

The primary research outcome was aggressive (invasive) breast cancers and mortality due to breast cancer. The researchers divided the data into two categories: screen-identified diagnoses and non-screen-identified diagnoses. They excluded women with prior invasive cancer, age ≥90 years, or without histological evidence of DCIS, and those with invasive breast cancer or chemotherapy within six months of diagnosis, inconsistent records, and fewer than 6.0 months of follow-up.

The researchers investigated the observed numbers and rates of invasive breast cancers, breast cancer deaths, and non-breast cancer deaths in England and Wales. They also computed cumulative predicted numbers and hazards based on cancer incidence and death rates for five-year age groups and individual calendar years. The researchers performed Poisson regression modeling to investigate variability in the observed-to-expected mortality rate ratio. They also investigated competing causes of death using five-year age-specific mortality rates.

Results

In 2018, 3,651 women in England acquired invasive breast cancers, which was >4.0-fold higher than predicted by national cancer incidence (NCI) statistics (the observed-to-anticipated rate ratio was 4.2). In women aged less than 45 to 70 years, the risk of getting invasive breast cancers remained elevated throughout the study. The cumulative odds of invasive-type breast cancers over 25 years were 27%, 25%, 22%, and 21% for those aged <45, 45 to 49, 50 to 59, and 60 to 70 years, respectively.

In total, 908 females died from breast cancer, which is about four-fold higher than the predicted rate based on the rates of breast cancer mortality among the general public. Throughout the follow-up period, the observed to anticipated breast cancer death rate ratio remained elevated. The cumulative mortality risk from breast cancer over 25 years was 7.6% based on the age of DCIS diagnosis. 5.8%, 5.9%, and 6.2% for under 45 years, 45 to 49 years, 50 to 59 years, and 60 to 70 years, respectively.

Among females aged 50 to 64 years who were eligible for NHS breast screening, the observed predicted rate of aggressive breast cancers among females with DCIS unidentified during screening was 1.3, whereas the breast cancer mortality ratio was 1.4.

Among 22,753 females with unilateral DCIS undergoing surgical procedures, those undergoing mastectomy instead of breast-conserving surgeries (BCS) had a reduced 25.0-year cumulative risk of ipsilateral aggressive breast cancers (mastectomy, 8.20%), BCS with radiotherapy (RT) 20%, and BCS without RT 21%. However, the decreases did not result in a decreased 25.0-year cumulative risk of breast cancer mortality (mastectomy, 6.50%; BCS with RT, 8.60%; BCS without RT, 7.80%).

By June 30, 2018, 27,543 women in England had been diagnosed with screen-undetected DCIS as their primary cancer, with 22,753 having unilateral DCIS and undergoing surgery. The number of women diagnosed every year grew with each calendar year, with more than half diagnosed while they were younger than 50 or ≥71 years old and therefore not receiving screening invitations.

Conclusions

Overall, the study findings showed that females with non-screen-detected DCIS have a four-fold higher risk of aggressive breast cancers and mortality than the general public. These hazards were the highest for women under 50 or ≥71 years of age at diagnosis and continued for ≥25 years. Breast cancer fatality chances are higher for women under 45 and over 60 years old.

Women with DCIS unidentified during screening had a higher cumulative risk of aggressive breast cancers and mortality, but the absolute differences were minor after 25 years. Mastectomy was related to a lower incidence of aggressive breast cancers than BCS, even when combined with RT. However, the odds of death from breast cancers were comparable between mastectomy and BCS with or without RT.