No benefit to adding ibandronate to hormonal therapy in postmenopausal breast cancer
The addition of ibandronate to adjuvant hormonal therapy provides no benefit to postmenopausal women with HR-positive breast cancer, according to early results from the phase III TEAM IIB trial (BOOG 2006-4)*.
Three years after randomization, the incidence of disease-free survival (DFS) was 94.3 percent among women given the bisphosphonate ibandronate in addition to hormonal therapy compared with 90.8 percent in women on hormonal therapy only (hazard ratio [HR], 0.80, 95 percent confidence interval [CI], 0.58–1.10). The 20 percent improvement in DFS experienced by women on ibandronate was insignificant. [SABCS 2016, abstract S6-02]
“Data from TEAM IIB showed that postmenopausal women who received ibandronate for three years along with hormone therapy had a trend toward improved DFS outcome that was statistically insignificant,” said Professor Sabine Linn from the Netherlands Cancer Institute in Amsterdam, Netherlands, who presented the findings at the San Antonio Breast Cancer Symposium (SABCS 2016) in Texas, US.
All-cause mortality was similar between patients on ibandronate (n=48) and hormonal therapy (n=47), while death due to breast cancer was higher in the hormonal therapy group (61.7 percent; n=29) compared with the ibandronate group (35.4 percent; n=17). There were 14 and 9 deaths due to secondary malignancies in the ibandronate and hormonal therapy groups, respectively (29.2 percent vs 19.1 percent).
Bone metastasis occurred in 1.6 percent (n=8) of patients in the ibandronate group compared with 4.7 percent (n=23) of those on hormonal therapy only (HR, 0.65, 95 percent CI, 0.38–1.11). Again, the 35 percent reduction in bone metastasis risk among ibandronate recipients was insignificant.
There were 36 and 51 serious adverse events reported by 31 patients on ibandronate and 39 patients on hormonal therapy, respectively. Four patients on ibandronate developed osteonecrosis of the jaw, but there were no residual complaints posttreatment.
“Patients should discuss this adjuvant treatment with their physicians to outweigh the possible side effects from the possible gain in survival,” said Linn.
Between February 2007 and May 2014, 1,116 postmenopausal women with stage I-III HR-positive breast cancer were recruited from 37 hospitals in the Netherlands. They were randomized to receive hormonal therapy for at least 5 years (tamoxifen followed by exemestane for 2–3 years or exemestane for 5 years for women with high risk) with or without once-daily oral ibandronate (50 mg) for 3 years. After a median follow-up period of 4.6 years, there were 149 DFS events.
As 73 of the participants have yet to complete ibandronate therapy, the question remains as to whether the current findings are premature, as well as whether there were enough women enrolled to demonstrate a significant DFS difference, said Linn.
The researchers will be further analysing the data once the last patient reaches the 3-year follow-up period, and plan on following the patients for up to 10 years to determine long-term effects.