On the other hand, Perez said that aromatase inhibitors do carry a risk of increased joint aches and, more importantly, may cause bone loss. "The majority of patients do very well but we recommend patients have bone density tests before using these drugs. I would probably not use aromatase inhibitors in a patient with severe osteoporosis."

While per-tablet cost of aromatase inhibitors is higher than tamoxifen, Perez said that they are still cost-effective because they have fewer side effects requiring treatment and they result in increased overall survival.

"It's no question that these drugs are better for patients when compared with other hormone therapies," Perez said.