A new study shows palbociclib almost doubled the time patients survived breast cancer without seeing it spread or get worse.

Women treated with the drug along with a hormone lived more than 20 months longer on average before the cancer got worse, compared with slightly more than 10 months for women who just took the hormone therapy.

The study's chief investigator says the magnitude of benefit they're seeing "is not something commonly seen in cancer medicine studies," and refers to the drug's benefits as "groundbreaking."

If the FDA approves it, palbociclib could be on the market next year.

--Rob Archer