A new Pfizer-developed anti-cancer drug the first member of a new class of oncology drugs provided a longer progression-free period compared to the control group. Women with advanced breast cancer experienced 20 months of progression-free time compared to only 10 months for women in the placebo-treated comparison group.
Palbociclib acts by inhibiting the activity of two enzymes involved in cell division, thus slowing the proliferation of cancer cells. The palbociclib study involved 165 post-menopausal women who were receiving their first treatment for recurrent or metastatic breast cancer. Like about 60 to 65 percent of breast cancers, these were estrogen receptor-positive, and all the women in the trial took another drug initially to block the production of estrogen. Then, about half of them were given palbociclib.
Although the length of progression-free survival in the women treated with the new drug was encouraging, investigators noted that there was no statistically significant increase in survival time in the treated women. However, the trial was not set up to measure this, requiring a lot more study patients to show such a benefit. Of course, larger trials are now underway.
Dr. Richard S. Finn, a principal investigator in the study, said in an interview quoted in the New York Times, The magnitude of benefit we are seeing is not something commonly seen in cancer medicine studies.
Not all physicians were equally positive about the results. Dr. Eric P. Winer of the Dana-Farber Cancer Institute in Boston was also quoted This is a small Phase 2 trial not tiny, but not the kind of study that would typically lead to a change in practice.
ACSH s Dr. Gilbert Ross concurs with Dr. Winer. While these results are quite encouraging, they must be replicated in a larger study before we can rely on this treatment. Hopefully, such follow-up studies are already underway.