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Palbociclib – A novel drug for metastatic breast cancer

The issue which has been lingering on in the Breast cancer community in the last few days has been the significant clinical benefit shown by Palbociclib in patients with advanced breast cancer in a phase 2 clinical trial. The results of the PALOMA-1 trial were discussed in a recently concluded meeting of the American Association for Cancer Research.

Palbociclib is an inhibitor of cyclin-dependent kinases (CDK) 4 and 6 and it inhibits cell proliferation and cellular DNA synthesis by preventing cell-cycle progression from G1 to S phase. In simple terms, it prevents cell division.

In the trial, patients were randomly assigned to the combination of daily palbociclib 125 mg for 3 weeks followed by 1 week off plus continuous daily letrozole 2.5 mg, or to daily letrozole. Treatment continued until disease progression, unacceptable toxicity, or withdrawal from the study, and tumors were assessed every 2 months.

Patients with hormone receptor positive metastatic breast cancer, demonstrated a significantly better progression-free survival as compared to patients receiving only hormonal treatment. The progression-free survival was significantly better with palbociclib plus letrozole than with letrozole alone (20.2 vs 10.2 months; hazard ratio [HR], 0.488; BP = .0004).

Although there was a positive trend seen in the overall survival analysis as well but the survival data was not mature enough to be shared currently.

The drug was well tolerated and the most common adverse effects were neutropenia, leukopenia, fatigue, and anemia.

Although some people are claiming that this drug will turn out to be the next standard of care in metastatic breast cancer, others share a more guarded opinion. There have been quite a few drugs which have shown promise in phase 2 trials but have not performed well in subsequent phase three trials.

The phase 3 trial (PALOMA-2) is currently underway and only time will tell whether Palbociclib is really beneficial or not.

The other issues which Indian patients & doctors need to consider are:

1. Cost & availability of the drug in India; cost/ benefit ratio

2. Overall survival benefit


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