The Food and Drug Administration announced Wednesday that it has begun investigating the possible connection between breast implants and the increased risk of a rare form of cancer.
While the number of women who may develop the disease is small, there is apparently no way to identify those who are likely to develop it, making it a source of potential concern to all women with the implants.
Among women who do not have implants, the cancer -- anaplastic large cell lymphoma or ALCL -- develops in the breast tissue of about three out of 100 million women nationwide.
But among women who do have implants, FDA investigators say they have identified as many as 60 worldwide who have developed ALCL, out of an estimated global population of 5 million to 10 million women with implants.
The FDA did not provide an incidence number for women with implants who developed the disease in the United States alone.
The agency said the number of known cases was too few to draw a conclusion linking implants to the disease.
FDA officials emphasized the small risk and said women with implants don't need to do anything more than maintain vigilance.
The FDA advised women not to change their routine medical care but said they should consult a physician if they notice swelling, pain or lumps around implants after post-surgical healing.
"Women who are not showing any symptoms or problems require only routine follow-up. FDA is not recommending the routine removal of breast implants," said William Maisel, chief scientist and a deputy director of the FDA's medical device office.
ALCL is a treatable cancer of the immune system, and its occurrence in the breast does not equate to breast cancer, Maisel said.
"I think there's reason to be concerned about this, but there shouldn't be reason for panic," said Phil Haeck, president of the American Society of Plastic Surgeons. Signs of ALCL associated with implants "are pretty dramatic. There's a lot of swelling and pain. They won't miss it," Haeck said.
The FDA also will ask the two U.S. manufacturers of implants, Allergan Inc. and Mentor Worldwide, to update product labeling to include information about ALCL.
"We fully support FDA's efforts to gather additional data and study ALCL in patients with breast implants," Mentor said in a statement.
An Allergan spokeswoman said in a statement that when ALCL has occurred, "most of the patients have responded to a variety of treatments, including simple removal of the implant and surrounding scar capsule."
"A woman is more likely to be struck by lightning than get this condition," the statement said.