U.S. regulators withdrew approval of Roche AG's Avastin, the world's best-selling cancer drug, as a treatment for breast cancer, Bloomberg News reports today.

The drug, which earns $6.2 billion, or 14 percent of Roche's total annual sales, has not been shown to be safe and effective as a breast cancer treatment, according to a statement from the Food and Drug Administration. Avastin will remain an approved treatment for other cancers, including certain types of colon, lung, kidney and brain cancer.

The drug was approved for metastatic breast cancer in February 2008 under the condition of additional trials, but data showed that it had minimal results on tumor growth, according to the FDA.

Roche is already feeling the effects of the decision. Its shares declined 0.5 percent to close at 142.60 Swiss francs in Zurich.

What does this mean for women taking the drug? Insurers might stop paying, and patients would have to look for alternatives or pay out-of-pocket. Some doctors, however, may continue to prescribe Avastin for breast-cancer treatment, since it's approved for other diseases. Still, the drugmaker has said the FDA move could put as much as 800 million Swiss francs ($873 million) in revenue at risk.

For both the drug company and the patients, the FDA decision reminds us of a common conflict in medicine: the importance of getting it right against the need of sick patients to get the drug right now.

(Kirsten Salyer is the social media editor for Bloomberg View.)