The draft guidance means that both innovative drugs can be recommended as options for people with hormone receptor (HR) positive, human epidermal growth factor receptor 2 (HER2) negative locally advanced or secondary breast cancer.
One breast cancer charity is describing the decision as "life-changing" and "long-awaited".
Around 8,000 women in England could be eligible for treatment with either of the 2 drugs.
There are around 45,000 new cases of breast cancer in the country each year.
Palbociclib is made by Pfizer and is also known by the brand name Ibrance. Ribociclib is manufactured by Novartis and is known by its brand name Kisqali.
According to NICE, both drugs can stall the growth of the cancer for an extra 10 months on average. Despite uncertainties about how long they can extend overall survival, it concluded that some improvements were likely.
In February this year, NICE announced it would not be recommending palbociclib because the high costs outweighed its clinical effectiveness.
Professor Carole Longson, director of the centre for health technology evaluation at NICE, says in a statement: "We are pleased therefore that the companies have been able to agree reductions to the price of palbociclib and ribociclib to allow them to be made routinely available."
Details of the discounts are confidential. The list price of a cycle of treatment with palbociclib is £2,950 for 21 capsules. This is the same price for a cycle of treatment with 63 tablets of ribociclib.
Both drugs are given once-daily with an aromatase inhibitor. Aromatase inhibitors reduce levels of the hormone oestrogen, blocking its ability to fuel some breast cancers.
Palbociclib and ribociclib are the first of a new type of drug that slows the progression of cancer by inhibiting 2 proteins called CDK 4 and 6.
Giving patients extra time
Breast Cancer Now says today's decision will give thousands of women extra time before their condition gets worse. Chief executive Baroness Delyth Morgan says: "This is a life-changing and long-awaited step forward in treatment for many patients with metastatic breast cancer, potentially offering thousands of women the closest thing they would have to a cure in their lifetime."
Samia al Qadhi, chief executive of Breast Cancer Care, comments: "These 2 exciting treatments, when combined with other drugs, offers the precision to target certain types of incurable breast cancer and we've seen it put the brakes on its growth for as long as 2 years.
"This could mean being there to see your child start school or celebrating next Christmas with loved ones and allows people to carry on living their daily lives with few side-effects."
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