Pfizer scored the FDA’s first-ever approval of a cyclin-dependent kinase inhibitor Tuesday afternoon when the regulator approved Ibrance (palbociclib) for post-menopausal women with estrogen receptor-positive (ER-positive), human epidermal growth factor receptor 2 negative (HER2) metastatic breast cancer who have not received an endocrine therapy.

The approval is somewhat anticlimactic in that industry watchers thought the agency was leaning toward approving breakthrough therapy treatment once Pfizer said it was talking labels and that the FDA told the drugmaker the drug could skip an interim advisory panel review.

Ibrance is expected to cost around $9,850 per month, bringing the cost of a 17-month regimen to around $167,000. Leerink analyst Seamus Fernandez projected 2015 sales of around $150 million in a Wednesday research note and consensus estimates put peak sales at about $3.8 billion by 2020. Fernandez noted that his team sees a potential for an additional $10 billion market opportunity if Ibrance were to land indications for high-risk early-stage breast cancer and recurrent cancer.  

The drug’s approval shores up plans for what could become a standalone unit of Pfizer. The drugmaker has talked about splitting up after having financials for each potential unit on hand after 2017, and the drug is considered a cornerstone product for the venture.

However, analysts have long noted that Pfizer is not alone in the CDK space. ISI analyst Mark Schoenebaum estimated in his Tuesday note that that Pfizer may have a two-year lead over Eli Lilly’s LY2835219 and Novartis’s LEE011.