Bisphosphonates: 'New Addition' to Breast Cancer Treatment?

Kate Johnson

December 13, 2013

SAN ANTONIO — Adjuvant bisphosphonate treatment significantly improves breast cancer survival and reduces bone recurrence in postmenopausal women with early breast cancer, according to a meta-analysis reported here at the 36th Annual San Antonio Breast Cancer Symposium.

"We have finally defined a new addition to standard treatment," announced lead investigator Robert Coleman, MD, professor of oncology at the University of Sheffield in the United Kingdom. He emphasized that, as hypothesized, the benefits of this therapy were confined to postmenopausal women.

"There is absolutely no effect on mortality in premenopausal women, with a hazard ratio [HR] of 1.0," he reported. "But for postmenopausal women, we see a 17% reduction in the risk of death [HR, 0.83], which is highly statistically significant."

In terms of the absolute benefit, bisphosphonates decreased the breast cancer mortality rate from 18.3% to 15.2% in postmenopausal women (P = .004).

The separation of benefit by menopausal status was also seen in the bone recurrence data.

In premenopausal women, there is no significant effect on bone recurrence (HR, 0.93), whereas in postmenopausal women, there was a 34% reduction. The difference was "highly significant," said Dr. Coleman.

"I personally believe adjuvant bisphosphonates should be standard treatment in postmenopausal women with breast cancer," said Michael Gnant, MD, professor of surgery at the Medical University of Vienna, who was one of the study investigators. He spoke during a plenary session before the results were formally announced.

"This is an important analysis," said Rowan Chlebowski, MD, PhD, medical oncologist from the Harbor-UCLA Medical Center in Los Angeles.

"There will be a substantial increase in the use of bisphosphonates," he told Medscape Medical News after the presentation.

"The only question is whether people will accept this analysis as the final word." Dr. Chlebowski explained that some people might criticize the study as being a post hoc analysis of previous findings.

"You might find some mixed feelings about whether this should be accepted, but I think this will get people thinking," he said. Dr. Chlebowski previously reported a large observational study that demonstrated that postmenopausal women taking oral bisphosphonates for osteoporosis had a significantly lower risk for breast cancer.

Bisphosphonates were originally indicated for the treatment of osteoporosis, and include agents such as alendronate (Fosamax, Merck), ibandronate (Boniva, Genentech), risedronate (Actonel, sanofi-aventis), and zoledronic acid (Reclast, Novartis).

But they are also indicated for bone-related use in breast cancer patients, Dr. Chlebowski pointed out.

Because bisphosphonates "also have an indication for preventing bone loss associated with aromatase inhibitor use, they are already approved in this setting, and would prevent recurrences. It will be interesting to see if guideline panels" like these findings, he noted.

Why Postmenopausal Women Benefit

In the plenary session, Dr. Gnant acknowledged that the data on bisphosphonates to date have been mixed.

There are "many trials showing controversial results" for bisphosphonates in the context of breast cancer, he said. "When we put them all together in an unselected population, some show beneficial effects and some do not."

Dr. Gnant explained why bisphosphonates appear to be effective in older but not younger women. "When you confine your analysis to the low-estrogen environment, postmenopausal women, or women rendered menopausal by ovarian function suppression, we see that all these trials show a consistent benefit for these patients," he said.

"Essentially, this low-estrogen hypothesis as a prerequisite for adjuvant bisphosphonate activity means that we believe these treatments can silence the bone marrow microenvironment. However, this only translates to relevant clinical benefits in low-estrogen environments," he added.

More Study Details

The meta-analysis involved 36 trials of adjuvant bisphosphonates in breast cancer with 17,791 pre- and postmenopausal women.

The primary outcomes of the study were time to distant recurrence, local recurrence, and new second primary breast cancer (ipsilateral or contralateral), time to first distant recurrence (ignoring any previous locoregional or contralateral recurrences), and breast cancer mortality.

Planned subgroup analyses based on hypotheses generated from previous findings included site of recurrence, site of first distant metastasis, menopausal status, and type and schedule of bisphosphonate therapy, said Dr. Coleman.

With bisphosphonate therapy, there was a nonsignificant 1% reduction in breast cancer recurrence at 10 years in postmenopausal women, compared with premenopausal women (25.4% vs 26.5%), and "a small borderline advantage" for distant recurrence (20.9% vs 22.3%), he reported.

However, there was a significant benefit of bisphosphonates in bone recurrence in postmenopausal women (6.9% vs 8.4%; P = .0009), with no effect on nonbone recurrence.

There was no impact of bisphosphonates on local recurrence or cancer in the contralateral breast.

For distant recurrence, there was a 3.5% absolute benefit in postmenopausal women (18.4% vs 21.9%; P = .0003); for distant recurrence, there is was a significant improvement of 2.9% in bone recurrence (5.9% vs 8.8%; P < .00001).

There was no significant reduction in first distant recurrence outside bone, and risk reductions were similar, irrespective of estrogen-receptor status, node status, or use or not of chemotherapy.

"Adjuvant bisphosphonates reduce bone metastases and improve survival in postmenopausal women," concluded Dr. Coleman. "We have statistical security in this result, with a 34% reduction in the risk of bone recurrence (P = .00001), and a 17% — or 1 in 6 — reduction in the risk of breast cancer death (P =.004)."

The analysis struck a clear line between pre- and postmenopausal women — something that was revealed in a subgroup analysis the AZURE trial, which Dr. Coleman was involved in (N Engl J Med. 2011;365:1396-1405).

Because of this, he was asked about the validity of basing the current analysis on the AZURE hypothesis-generating population.

"We repeated the analysis without the AZURE patients, because they are the hypothesis-generating population, and the P values and risk reductions did not change," he explained.

The study was funded by Cancer Research UK, the UK Medical Research Council, and the Early Breast Cancer Trialists Collaborative Group. Dr. Coleman has disclosed no relevant financial relationships.

36th Annual San Antonio Breast Cancer Symposium (SABCS): Abstract S4-07. Presented December 12, 2013.

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