AMSTERDAM (FRONTLINE MEDICAL NEWS) – In real-life practice, women with early, localized breast cancer who underwent breast conserving therapy had better breast cancer–specific and overall survival compared with women who underwent mastectomy, according to investigators in the Netherlands.

Among nearly 130,000 patients treated over two different time periods, breast-conserving surgery and radiation (BCT) was associated with superior survival for women older than 50, patients who did not receive adjuvant chemotherapy, and those with comorbidities – irrespective of either hormonal or human epidermal growth factor receptor 2 (HER2) status, reported Mirelle Lagendijk, MD, of Erasmus Medical Center Cancer Institute in Rotterdam, the Netherlands.

For patients 50 and younger, overall survival (OS), but not breast cancer–specific survival (BCSS), was superior with the more conservative approach.

“Breast conserving therapy in these identified subgroups seems to be the preferable treatment when both treatments are optional,” Dr. Lagendijk said at an annual congress sponsored by the European Cancer Organisation.

Although recent observational studies have shown survival with BCT to be at least equivalent for women with early stage disease, there is still a lack of sufficient data on BCSS, potential confounders such as systemic therapies and comorbidities, and on the relative effects of BCT or mastectomy on subgroups, she said.

The investigators drew data from the Netherlands Cancer Registry on 129,692 patients with early, primary invasive breast cancer without metastases other than to regional lymph nodes (T1-2NO-2MO).

They compared BCT to mastectomy for BCSS and OS in the population as a whole and in subgroups based on prognostic factors. They controlled for age, tumor and nodal stage, comorbidities, systemic therapy, hormone receptor and HER2 status, differentiation grade, morphology, year of treatment, axillary lymph node dissection, and contralateral breast cancer.

They divided patients into two treatment time periods. The older cohort consisted of 60,381 patients treated from 1999 through 2005, 48% of whom underwent mastectomy, with a median follow-up of 11.1 years, and 52% of whom had BCT, with a median follow-up of 12 years.

The more recent cohort consisted of 69,311 patients, 40% of whom had mastectomy with a median follow-up of 5.9 years, and 60% of whom had BCT with a median follow-up of 6.1 years.

In both time periods, deaths from all causes were lower among patients treated with BCT. In the older cohort, 13,960 of 28,968 patients (48.2%) who underwent mastectomy had died, compared with 8,915 of 31,413 patients (28.4%) who underwent BCT. In the more recent cohort, 5,504 of 27,731 (19.8%) of patients who had mastectomies had died, compared with 3,702 of 41,580 (8.9%) who underwent BCT.

“Irrespective of the time cohort and irrespective of the treatment, around 50% of the events were breast cancer related,” Dr. Lagendijk said.

BCSS was superior with BCT in each time cohort (log-rank P less than .001 for each). In the earlier cohort, BCT was significantly superior for BCSS across all disease stages; in the later cohort, it was significant for all but stages T1N1 and T1-2N2.

BCSS was superior for patients in all age categories in the early cohort, and for patients 50 and older in the later cohort.

“The final stratification performed for comorbidities present in the patients evaluated showed, surprisingly, that especially for those patients with comorbidity, there was significantly better breast cancer-specific survival when treated by breast conserving therapy as compared to a mastectomy,” Dr. Lagendijk said.

The investigators acknowledged that the study was limited by its retrospective design, potential confounding by severity, and the inability to show causal relationship between survival and treatment type.

“There is a very good example of how we use large national registries to be able to pinpoint what is the difference [between treatments], what kind of information can we give to our patients,” said Peter Naredi, MD, of the University of Gothenburg, Sweden. Dr. Naredi, cochair of ECCO2017, spoke at a briefing prior to the presentation of the data in a plenary session.

Dutch health agencies sponsored the study. Dr. Lagendijk and Dr. Naredi reported no conflicts of interest.


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