The following article is part of conference coverage from the 17th St. Gallen International Breast Cancer Symposium, which is being held virtually from March 7-21, 2021. The team at Cancer Therapy Advisor will be reporting on the latest research conducted by leading experts in breast cancer. Check back for more from the 17th St. Gallen International Breast Cancer Symposium.

Women with breast cancer who underwent breast-conserving surgery with postoperative radiotherapy were found to have better survival than those who received mastectomy, regardless of radiotherapy, according to the results of a Swedish study presented at the 17th St. Gallen International Breast Cancer Conference 2021.

These results indicate that “when both interventions are valid options for the individual patient, mastectomy should not be regarded as equal to breast conservation,” according to Jana de Boniface, MD, PhD, of Karolinska Institute, Stockholm, Sweden, and colleagues.

According to the poster presentation, recent studies indicated that breast-conserving surgery with radiotherapy resulted in better survival than mastectomy without radiotherapy; however, the data did not indicate if this was an independent effect or a consequence of selection bias.

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To explore this further, the researchers conducted a prospective study that included 48,986 women from national registries in Sweden. All of the women were diagnosed with primary invasive T1-2 N0-2 breast cancer between 2008 and 2017. Treatments included breast-conserving surgery plus radiotherapy (59.9%), mastectomy without radiotherapy (25.3%), or mastectomy with radiotherapy (14.7%).

The investigators presented their results after a median follow-up of 6.28 years. Overall 5-year survival was 91.1%, with a 5-year breast cancer-specific survival of 96.3%.

The data were adjusted for all pivotal confounders of comorbidity and socioeconomic status including age, calendar year, residence, grade, TNM (tumor, node, metastasis) classification, subtype, education, family income, and country of birth.

After these adjustments, overall survival and breast cancer-specific survival were found to be significantly worse for women who underwent mastectomy without radiotherapy (hazard ratio [HR] 1.79; 95% CI, 1.66-1.92 and HR 1.66; 95% CI, 1.45-1.90) and mastectomy plus radiotherapy (HR 1.24; 95% CI, 1.13-1.37 and HR 1.26; 95% CI, 1.08-1.46) compared with breast-conserving surgery plus radiotherapy.

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De Boniface J, Szulkin R, Johansson ALV. Survival after breast conservation versus mastectomy adjusted for comorbidity and socioeconomic status: national 6-year follow-up on 48986 women. Poster presented at:  17th St Gallen International Breast Cancer Conference; March 17-21, 2021. Abstract P127.