Phase II Study Shows New Medicine May Slow Metastatic Breast Cancer

Breast Cancer News
April 17, 2014
Nicole Katze, MA, Editor and Manager, Content Development
Reviewed By: 
Adam Brufsky, MD, PhD

Research presented at the 2014 American Association for Cancer Research Annual Meeting suggests a new treatment pair may help double the time before estrogen receptor-positive, metastatic breast cancer grows or spreads.

The findings come from phase II of the PALOMA-1 trial.  Researchers compared the effects of the aromatase inhibitor letrozole (Femara) combined with a new medicine under study called palbociclib, versus letrozole alone. An early report on the medicine’s promise was presented at the 2012 San Antonio Breast Cancer Symposium.

Background and Goals

Palbociclib, called PD-991 in earlier studies, targets an enzyme that plays a part in cell division and growth, called kinase. Cyclin-dependent kinase (CDK) 4 and 6 are two that help tumor cells grow. Researchers believe using palbociclib to stop CDK 4 and 6 from doing so may slow the growth or spread of metastatic breast cancer.

Aromatase inhibitors, AIs, like letrozole are the standard of care for women with ER-positive disease who are postmenopausal, or no longer get their periods due to age, surgery or medicine. AIs block the enzyme aromatase to stop the body from making the estrogen that ER-positive cancer needs to grow.

This latest report on PALOMA-1 shared progression-free survival, PFS, findings from both halves of the trial. In the earlier analysis, only part 1 was analyzed. Progression-free survival is the time from when the trial medicine is first taken to the cancer growing or spreading.

Read more about part 1 here.


 A total of 165 women joined the trial between the two parts. Women were given either:

  • palbociclib daily for 3 weeks, followed by 1 week off, plus daily letrozole
  • a placebo, an inactive pill, taken daily for 3 weeks, followed by 1 week off, plus daily letrozole

Letrozole and palbociclib were both taken by mouth. Women continued this treatment until side effects became too dangerous, the cancer progressed or they left the trial. All who took part were postmenopausal.

In part 2, the researchers also collected data on two genetic markers, CCND1 and p16, to see if they were related to how well palbociclib worked.


The final results showed women in the palbociclib plus letrozole group had a PFS rate of about 20.2 months, while the letrozole only group had a PFS rate of about 10.2 months. Though it’s too early to calculate overall survival, the time from the start of treatment to death from any cause, some early analysis suggests a longer survival time among those taking palbociclib plus letrozole. A phase III trial is underway to explore this further.

At the close of part 2, the research team found that neither genetic marker has an impact on whether palbociclib works or not.

What This Means for You

Phase II trials do not lead to the immediate approval of a new medicine for use, so the present results of PALOMA-1 will not make palbociclib available right away. However, successful phase II trials give researchers reason to plan phase III trials, through which new medicines can gain FDA approval.

Early findings from PALOMA-1 led the FDA to give it breakthrough therapy designation in 2013, a status that helps researchers study and develop new medicines faster. 

If you are a postmenopausal woman with metastatic breast cancer and are interested in treatment with palbociclib, talk with your doctor about open clinical trials. Two trials, NCT01942135 and NCT01740427, both listed on, are enrolling.

Finn, R., Crown, J., Lang, I., etal. Final results of a randomized phase II study of PD 0332991, a cyclin-dependent kindase (CDK)-4/6 inhibitor, in combination with letrozole vs letrozole alone for first-line treatment of ER+/HER- advanced breast cancer (PALOMA-1; TRIO-18).Paper presented at: American Association of Cancer Research Annual Meeting; April 2014; San Diego, CA.

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