In the past decade in the United States, use of double mastectomy has more than doubled in the surgical treatment of women with ductal carcinoma in situ (DCIS), said a presenter at the annual meeting of the American Society of Breast Surgeons in Las Vegas, Nevada.
But there's a problem — very few studies have examined the risk for breast cancer occurring in the opposite breast among cases of single-breast DCIS, said Megan Miller, MD, a surgeon from Memorial Sloan Kettering Cancer Center in New York City.
Furthermore, few data exist on what risk factors contribute to any would-be contralateral breast cancer occurrence, she added.
Into that information breach comes a new study from Dr Miller and New York colleagues. "There is a low risk of contralateral breast cancer after DCIS treated with breast-conserving surgery," she said, summarizing study findings during a presscast from the meeting.
Among the 2759 study patients with ipsilateral DCIS (all of whom underwent lumpectomy between 1978 and 2011), 127 developed a contralateral cancer (either DCIS or an invasive cancer). The 5- and 10-year occurrence rates were 3.2% and 6.4%, respectively. Median follow-up was 6.8 years.
These low rates suggest that "ipsilateral DCIS should not prompt a bilateral mastectomy," Dr Miller said in a press statement.
"Bilateral mastectomy in the setting of unilateral DCIS should be the exception rather than the routine," said Julie Margenthaler, MD, a surgeon at Washington University School of Medicine in St. Louis, who moderated the presscast.
Bilateral mastectomy in the setting of unilateral DCIS should be the exception. Dr Julie Margenthaler
However, with regard to ipsilateral recurrence, the new findings are nuanced, because some cases of DCIS are more likely to recur in the same breast than others. "For these patients, examining risk factors for recurrence and the benefits of radiation and endocrine therapy to treat the existing cancer are important," commented Dr Miller.
Dr Margenthaler reminded clinicians that the American Society of Breast Surgeons has consensus guidelines that can help them discuss these complex treatment decisions with patients.
The only factor that affected the occurrence of contralateral cancer was endocrine therapy (P = .03), Dr Miller reported.
"Women who received tamoxifen or aromatase inhibitors had about half the risk of cancer in the opposite breast as those who did not at 10 years after surgery," she said. "That's not surprising because these are systemic therapies and will affect both breasts equally."
Specifically, endocrine therapy reduced the 10-year risk for same-breast recurrence (7.8% vs 16.3% among patients who had no endocrine therapy) and contralateral cancer (3.2% vs 6.4%).
In sum, the study data suggest that patients and clinicians "should focus on risk factors and appropriate therapy for the diseased breast, not the opposite breast," said Dr Miller.
Dr Miller said the new study is "unique" because it not only looked at the rate of contralateral cancer after initial treatment but also compared the competing risks for contralateral disease and ipsilateral breast tumor recurrence
In that analysis of the cumulative competing risks, recurrence was more than twice as likely as development of a new cancer in the opposite breast — at both 5 and 10 years (7.8% vs 2.9% and 14.5% and 5.8%, respectively).
The study also assessed whether risk factors for ipsilateral breast tumor recurrence were associated with risk for a contralateral breast cancer, said Dr Miller.
She reported that her team did not find any correlations between the development of new contralateral tumors and patient variables that might be expected to be related — including younger age, positive family history of breast cancer, higher nuclear-grade disease, clinical presentation, and earlier treatment.
However, a number of these factors were associated with cancer returning in the same breast.
Clinically Detected Disease More Likely to Recur in Same Breast
Importantly, DCIS that was found clinically (via a palpable mass, nipple discharge, or the occurrence of Paget's disease) recurred in the same breast more often than mammographically detected disease (10-year rate: 20.1% vs 13.5%).
Postsurgical radiation also significantly reduced the rate of ipsilateral breast tumor recurrence compared to no radiation (10-year rate: 10.3% vs 19.3%).
Same-breast tumor recurrence was also lower in those treated more recently (12.9% for treatment in 1999 or later vs 19.3% for treatment in 1998 or earlier), owing to improvement in therapy.
In their abstract, the study authors concluded: "Identification of factors associated with higher ipsilateral breast tumor recurrence risk may be important in decision-making between breast conserving surgery and unilateral mastectomy, but should not prompt contralateral prophylactic mastectomy for DCIS."
Dr Miller and Dr Margenthaler have disclosed no relevant financial relationships.
American Society of Breast Surgeons 18th Annual Meeting. Presented April 28, 2017.
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