Here's Why Blueprint Medicines Fell as Much as 15.1% Today

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What happened

Shares of clinical-stage biopharma Blueprint Medicines (NASDAQ: BPMC) dropped over 15% today after the company reported data from a phase 1 trial for BLU-667 in patients with three types of cancers in which the RET gene is overexpressed. The gene-targeting approach elicited tumor shrinkage in 84% of patients taking the drug candidate, although only 45% of responses across the study were considered significant.

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Wall Street seems to be taking issue with how the drug candidate appeared to fare in each of the three types of cancers studied. The preliminary data show BLU-667 delivered the lowest response rate in the most common RET-altered cancer, but analysts could be overreacting.

As of 12:10 p.m. EDT, the stock had settled to a 13.3% loss. The stock is up 355% in the last three years.

So what

Blueprint Medicines is investigating whether BLU-667 can become a treatment for cancers expressing the RET gene. While many different tumor types have been shown to utilize the gene, the current phase 1 trial started by looking at three cancers: non-smal-cell lung cancer (NSCLC), medullary thyroid cancer (MTC), and papillary thyroid cancer (PTC).

There were 14 evaluable patients with NSCLC, 25 with MTC, and one with PTC. The overall response rates were 50% for the evaluable patients with NSCLC, 40% for the evaluable patients with MTC, and 100% for PTC (there was only one evaluable patient).

Wall Street seems to be concerned with the overall response rates for MTC. That's because RET-altered cancers represent nearly 60% of all MTC cases, but only 1% to 2% of NSCLC cases. In other words, analysts are already looking ahead to the potential patient populations that could be treated with an RET-gene-targeting therapy.

Now what

Of course, the data were reported from an early-stage trial, so it seems a little silly to draw firm conclusions about the 40% overall response rate. The number will change -- for better or for worse -- as the trial expands to include more patients. Some analysts think Blueprint Medicines will achieve even better response rates in the future, because the phase 1 trial was aimed at evaluating the safety of BLU-667, not optimizing its dose. But there was a dose-dependent response, so putting more patients on higher doses could result in a higher overall response rate.

For now, investors should be encouraged by the results from the early-stage trial while not forgetting that there's a long way to go. That said, the emergence of gene-targeted therapeutic drug candidates appears to be a positive trend for the industry, patients, and investors.

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Maxx Chatsko has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.