Swedish DCIS cohort links breast conservation with favorable survival outcomes

A nationwide Swedish cohort study of 7,165 women with ductal carcinoma in situ found that breast-conserving surgery followed by radiotherapy was associated with better overall survival than mastectomy without radiotherapy among women aged 70 or older. In the same age group, breast-conserving surgery without radiotherapy was also associated with higher overall mortality than breast-conserving surgery with radiotherapy. The observational study does not establish that treatment caused the survival differences, and its all-age findings varied between complete-case and multiple-imputation analyses.

Ductal carcinoma in situ, or DCIS, is a noninvasive breast cancer in which malignant cells are contained within the basement membrane. Treatment can involve breast-conserving surgery or mastectomy, with radiotherapy used after some breast-conserving operations. Researchers linked the Swedish National Quality Register for Breast Cancer with the Cause of Death Register, National Patient Register, Total Population Register and socioeconomic database to examine outcomes among women with primary DCIS treated in Sweden from 2008 through 2019. The three compared groups were breast-conserving surgery with radiotherapy, mastectomy without radiotherapy and breast-conserving surgery without radiotherapy.

Of the 7,165 women included, 3,821, or 53.3%, received breast-conserving surgery with radiotherapy; 2,381, or 33.2%, underwent mastectomy without radiotherapy; and 963, or 13.4%, received breast-conserving surgery without radiotherapy. The researchers stratified participants into ages below 60, 60 to 69 and 70 or older; 1,387 women, representing 19.4% of the cohort, were at least 70. Screening detection was more common below age 70, while comorbidity scores of two or more were more frequent among women aged 70 or older. Those receiving breast-conserving surgery with radiotherapy were also more likely to be married or partnered, have higher education and income, and have no recorded comorbidity.

During a median follow-up of 71.7 months for death, 383 participants died, including 40 whose death was attributed to breast cancer. The estimated 10-year overall survival for the full cohort was 90.4%, with a 95% confidence interval of 89.3% to 91.5%. It was 93.1% for breast-conserving surgery with radiotherapy, 88.0% for mastectomy without radiotherapy and 86.3% for breast-conserving surgery without radiotherapy. Estimated 10-year breast cancer–specific survival was 98.8% overall and was similar across the three groups. Because there were too few breast cancer deaths for further adjusted regression analysis, the principal survival comparisons evaluated death from any cause.

Results for the entire cohort depended partly on how missing data were handled. After stepwise adjustment for age, diagnosis year, region, histopathological extent, detection method, nuclear grade, education, family income, marital status, country of birth and comorbidity, mastectomy without radiotherapy was associated with higher overall mortality in the complete-case analysis, with a hazard ratio of 2.10 and a 95% confidence interval of 1.20 to 3.67. In the multiple-imputation analysis, however, the fully adjusted association was not statistically significant, with a hazard ratio of 1.29 and a 95% confidence interval of 0.95 to 1.76. The complete-case cohort also had fewer events and was selected toward later diagnosis years with shorter follow-up.

Breast-conserving surgery without radiotherapy was associated with higher overall mortality than breast-conserving surgery with radiotherapy in both analytical approaches after full adjustment. The hazard ratio was 2.68, with a 95% confidence interval of 1.34 to 5.34, in the complete-case analysis and 1.72, with a 95% confidence interval of 1.23 to 2.39, in the multiple-imputation analysis. A sensitivity analysis restricted to women with a comorbidity score of zero or one left the overall-death estimates largely unchanged. Another sensitivity analysis that censored follow-up at contralateral breast cancer produced somewhat stronger treatment associations, including a significant mastectomy association after adjustment for comorbidity in the multiple-imputation analysis.

The clearest age-specific survival pattern occurred among women aged 70 or older. In this group, mastectomy without radiotherapy was associated with higher overall mortality than breast-conserving surgery with radiotherapy in both analyses: the complete-case hazard ratio was 2.48, with a 95% confidence interval of 1.09 to 5.62, and the multiple-imputation hazard ratio was 1.89, with a 95% confidence interval of 1.23 to 2.90. Omission of radiotherapy after breast-conserving surgery was also associated with higher mortality among women aged 70 or older in the multiple-imputation analysis, with a hazard ratio of 2.32 and a 95% confidence interval of 1.47 to 3.68, although the corresponding complete-case estimate was not statistically significant. Among women aged 60 to 69, omission of radiotherapy was associated with higher mortality in both analyses. No significant overall-mortality difference among the three treatment groups was detected below age 60.

Local recurrence remained uncommon in absolute terms but followed a different pattern from overall survival. The study registered 318 local recurrences within 10 years: 204 after breast-conserving surgery with radiotherapy, 32 after mastectomy without radiotherapy and 83 after breast-conserving surgery without radiotherapy. The estimated 10-year local recurrence probability was 7.2% for the full cohort, with a 95% confidence interval of 6.3% to 8.0%. Local recurrence–free survival was 90.9% after breast-conserving surgery with radiotherapy, 97.8% after mastectomy without radiotherapy and 87.4% after breast-conserving surgery without radiotherapy. In adjusted multiple-imputation analyses, mastectomy was associated with lower recurrence risk than breast-conserving surgery with radiotherapy, with a hazard ratio of 0.18 and a 95% confidence interval of 0.11 to 0.28, while omission of radiotherapy was associated with higher risk, with a hazard ratio of 1.79 and a 95% confidence interval of 1.31 to 2.46.

The increased recurrence risk associated with omitting radiotherapy was most pronounced among women aged 60 or older. In contrast, the lower recurrence risk associated with mastectomy compared with breast-conserving surgery with radiotherapy remained statistically significant only among women below 60. An exploratory analysis applying NRG Oncology/RTOG 9804 risk criteria recorded eight local recurrences among 160 high-risk cases and five among 196 low-risk cases. Overall mortality did not differ significantly between those exploratory risk groups, with a log-rank P value of 0.23. The authors emphasized that the recurrence and overall-survival findings do not point in the same direction: mastectomy had the lowest observed recurrence risk, whereas breast-conserving surgery with radiotherapy combined a low absolute recurrence rate with the highest overall survival, particularly in older women.

Several limitations constrain interpretation of the registry analysis. Treatment was not randomized, and women in the three groups differed in education, income, screening detection and comorbidity, creating the possibility of residual selection bias. The study adjusted for measured patient, tumor and socioeconomic factors, but information on smoking, obesity, margin status and genetic susceptibility was unavailable. Multiple imputation addressed missing histopathological extent and nuclear grade under an untestable missing-at-random assumption. Register data also could not consistently distinguish noninvasive from invasive local recurrence or standard from oncoplastic breast-conserving surgery. The researchers therefore described the results as associations, not proof that breast-conserving surgery with radiotherapy causes superior survival. Within those limits, the study found favorable overall-survival outcomes and a low absolute recurrence risk for the combination, with the strongest observed survival associations occurring among women aged 70 or older.

Subject of Research: Age-specific overall survival and local recurrence after breast-conserving surgery, mastectomy and radiotherapy for ductal carcinoma in situ

Article Title: Age-specific survival after breast conservation versus mastectomy for ductal carcinoma in situ of the breast

Article References: de Boniface, J., Szulkin, R., Karlsson, P., & Johansson, A. L. V. (2026). Age-specific survival after breast conservation versus mastectomy for ductal carcinoma in situ of the breast. Breast Cancer Research and Treatment, 220(1), Article 10. https://doi.org/10.1007/s10549-026-08097-y

Image Credits: AI Generated

DOI: 10.1007/s10549-026-08097-y

Keywords: ductal carcinoma in situ, breast-conserving surgery, mastectomy, radiotherapy, overall survival, local recurrence, older women, Swedish cohort, observational study, population-based research, Age-specific, survival