Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

Let's take a look at four stocks -- Insmed (INSM -1.93%), Exelixis (EXEL 0.13%), United Therapeutics (UTHR 0.42%), and Alnylam (ALNY -0.52%) -- which could all loom large in health care headlines this morning.

Insmed's lung infection drug fails a mid-stage trial
Insmed is down 9% in premarket this morning after reporting that its lung infection drug, Arikayce/Arikace, failed to meet the main goal of a phase 2 trial on patients with nontuberculous mycobacterial lung infections. Insmed does not have any marketed products.

This setback is a devastating blow for Insmed, since Arikayce is the company's only pipeline product. The drug was being tested for three kinds of lung infections. The most advanced indication, pseudomonas aeruginosa lung infections in cystic fibrosis patients, has reached phase 3 trials in Europe and Canada. The third indication, for pseudomonas aeruginosa lung infections in non-cystic fibrosis patients, has completed a phase 2 study.

Piper Jaffray, which reiterated its Overweight rating on the stock, noted that although the study failed to meet its primary endpoint, it met a "much more meaningful and clinically relevant" secondary endpoint of culture conversion.

Exelixis plunges after reporting the completion of an interim analysis
Meanwhile, Exelixis, which just reported the European approval of Cometriq yesterday, is down 30% in premarket this morning. Exelixis announced that an Independent Data Monitoring Committee (IDMC) had notified the company that a planned interim analysis of the COMET-1 phase 3 pivotal trial had been completed, and that the IDMC has recommended that the trial proceed to its final analysis. The company also stated that it continues to anticipate top-line data from the COMET-1 trial later this year.

COMET-1 is Exelixis' closely watched trial testing Cometriq as an advanced prostate cancer treatment, a potentially major indication for the drug.

United Therapeutics' Remodulin is approved in Japan
United Therapeutics just announced that Japan's Ministry of Health, Labor, and Welfare has approved Remodulin, its injected treatment for pulmonary arterial hypertension (PAH).

The drug will be sold in Japan under the brand name Treprost by Mochida Pharmaceutical, which previously signed an exclusive distribution agreement with United Therapeutics. Sales of Remodulin and Tyvaso, an inhaled version of the drug, accounted for 83% of the company's top line in fiscal 2013.

Orenitram, a new oral drug which contains the same active ingredient as Remodulin and Tyvaso, was approved last December and is expected to generate peak sales of $200 million to $300 million -- which could be a big boost for a company which reported $1.1 billion in revenues in 2013.

Sanofi boosts its investment in Alnylam
Last but not least, Sanofi's (SNY 2.00%) Genzyme unit just boosted its investment in Alnylam Pharmaceuticals, which studies RNAi therapeutics. Genzyme, which is focused on rare disease and multiple sclerosis treatments, exercised its right to buy 344,448 unregistered shares of Alnylam common stock.

Based on Alnylam's closing price of $66.88 on March 25, the transaction is valued at approximately $23 million. Genzyme now owns 12% of Alnylam's common stock. The two companies have been partnered since January in the development and commercialization of RNAi therapeutics as genetic medicines. Under that agreement, Genzyme purchased 8.8 million shares of new Alnylam stock for approximately $80 per share.

Alnylam doesn't have any marketed products, but its pipeline of a wide variety of genetically targeted treatments for amyloidosis, hemophilia, hypercholesterolemia, iron overload disorders, hyperlipidemia, and other indications.

Sanofi's investment in Alnylam is significant, since it has a history of investing in promising next generation technologies, such as its partnership with Regeneron in the development of fully human monoclonal antibodies. Sanofi recently considered raising its stake in Regeneron from 16% to 30%. This recent vote of confidence for Alnylam could increase bullish interest in the company, which has already rallied 180% over the past 12 months.