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Shares of  Puma Biotechnology, Inc. (PBYI - Snapshot Report) declined significantly on Jun 2 to end the day’s trading at $57.06 following the disappointing performance of its oncology candidate PB272 (neratinib) in an ongoing phase II study. The study, which is being performed by the Translational Breast Cancer Research Consortium, is evaluating the candidate for treating patients with HER2 positive metastatic breast cancer that has metastasized to the brain.

Puma Biotech presented data from the first cohort of 40 patients from the multicenter study at the annual American Society of Clinical Oncology (ASCO) meeting. The first cohort included patients with progressive brain metastases. They were being treated with PB272 as a monotherapy. The company is enrolling patients for the second and third cohorts of the study.

The second cohort will include 5 patients with brain metastases who are amenable to operation. They will be treated with PB272 as a monotherapy before and after surgical resection. The third cohort will include 60 patients with progressive brain metastases. They will be treated with Puma Biotech’s oncology candidate in combination with Roche’s (RHHBY - Analyst Report) Xeloda (capecitabine).

Side Effects Hurt Stock

Data from the first cohort of the study revealed that treatment with PB272 caused grade 3 diarrhea in many patients. Some of the 40 evaluated patients also experienced grade 2 diarrhea.

Modest Efficacy Results Fail to Please Investors

Efficacy results from the trial were far from impressive with only 3 of the 40 patients in the first cohort demonstrating a partial response to treatment by PB272. Data also revealed that only 10% patients experienced prolonged stable disease (in excess of 6 months), and 30% demonstrated stable disease of less than or equal to 6 months.  Moreover, median data with respect to progression-free survival and overall survival were found to be 1.9 months and 8.7 months , respectively, following treatment with Puma Biotech’s candidate.

We believe investor focus will remain on PB272, which is being evaluated in other studies as well, going forward.

Another Breast Cancer Candidate Fails

Puma Biotech was not the only company to report below-par results from a study on a breast cancer candidate. GlaxoSmithKline (GSK - Analyst Report) reported that its drug Tykerb in combination with Roche’s Herceptin failed to meet the primary end point of improved disease free survival (DFS) in a phase III study for treating adjuvant (early stage) breast cancer. 

The failure of Glaxo’s Tykerb in the adjuvant setting is not good news for PB272 which is being developed for the treatment of HER2 positive metastatic (advanced) breast cancer.

Puma Biotech, a biopharmaceutical company, carries a Zacks Rank #4 (Sell). Gilead Sciences (GILD - Analyst Report) is an example of a better-ranked stock in the biopharma space, with a Zacks Rank #1 (Strong Buy).

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