Bilateral Mastectomy in DCIS May Be Overtreatment

Women who undergo bilateral mastectomy for the treatment of ductal carcinoma in situ (DCIS) may be overtreated, according to the results of a study presented at a press conference ahead of the 2017 American Society of Breast Surgeons Annual Meeting. The study showed that only a small percentage of women with this early, non-invasive breast cancer who underwent breast conserving surgery instead of double mastectomy developed a contralateral cancer after 5 years.

“There is a low risk of contralateral breast cancer after DCIS for women treated with breast conserving surgery and this risk is low irrespective of age, family history, and characteristics of initial DCIS,” said Megan Miller, MD, of Memorial Sloan Kettering Cancer Center in New York, who presented the results during the press conference.

According to Miller, overall survival after treatment for DCIS is excellent, yet many patients overestimate both their risk of local recurrence and their risk for contralateral breast cancer, potentially leading to decisions in favor of bilateral mastectomy. Despite a rising incidence in the use of bilateral mastectomy for these women, few studies have examined the risk for contralateral breast cancer in women with DCIS treated with breast conserving surgery, she said.

Therefore, Miller and colleagues used a prospectively maintained database to evaluate women with DCIS who underwent breast conserving surgery between 1978 and 2011 at MD Anderson. The study included more than 2,750 women.

For women who underwent breast conservation, only 3.2% developed contralateral disease at 5 years and 6.4% at 10 years. A multivariable analysis of risk factors associated with contralateral disease showed no association with age, family history, and characteristics of initial DCIS; however, endocrine therapy was associated with increased risk (HR, 0.57; 95% CI, 0.35–0.93; P = .03).

The researchers also compared the risk of contralateral breast cancer with the risk of ipsilateral breast tumor recurrence (IBTR), and whether risk factors for IBTR were associated with risk of contralateral disease.

For the 331 patients with IBTR, they evaluated risk from the time of recurrence to subsequent contralateral breast cancer and found that rates of contralateral disease were similar to that of the whole cohort (5-year risk for patients with IBTR 3.7% vs 3.2% for entire population; 10-year risk: 8.1% vs 6.4%).

Looking at competing risk where only the first event was counted, the risk for ipsilateral recurrence was 2.5 times greater than contralateral recurrence (5-year: 7.8% vs 2.9%; 10-year: 14.5% vs 5.8%).

Among women who had no radiation, the competing risk for ipsilateral disease at 10 years was almost four times greater than for contralateral disease (19.5% vs 5.2%). A multivariable analysis showed that there was no risk factor that was significantly associated with contralateral risk, although the use of endocrine therapy approached statistical significance. In contrast, nearly all known risk factors were strongly associated with ipsilateral recurrence, Miller said.

“While factors associated with IBTR risk are important in decision-making regarding management of initial DCIS, they are not an indication for contralateral prophylactic mastectomy,” Miller concluded.