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.

What: Shares of Retrophin (NASDAQ:RTRX), a predominantly clinical-stage biopharmaceutical company focused on the development of therapies to treat rare disease, tumbled as much as 12% on Wednesday following a Form 4 filing with the Securities and Exchange Commission that showed CEO Martin Shkreli sold shares of common stock.

So what: All company insiders, including CEOs, are required to report purchases and sales of common stock, and shareholders were none too pleased to discover that Shkreli on May 30 sold 292,400 shares of Retrophin stock at $15.14 per share for a net proceed of more than $4.4 million. The sale, which was filed on June 3 with the SEC, represented approximately 9.3% of Shkreli's total holdings in the company. Because insiders are believed to understand the inner workings of their company better than any Wall Street analyst or investor, seeing one of the most prominent figures selling off a greater than 9% stake in Retrophin is a bit unnerving for shareholders.

Now what: Generally speaking, I wouldn't place too much credence in insider buys and sells, which can be undertaken for tax purposes or a myriad of other reasons. Insider moves are often short-term share-price drivers and rarely affect the long-term investing thesis in a business. Shareholders should really focus on whether Retrophin can narrow its losses. Retrophin's recently announced licensing agreement for kidney stone prevention treatment Thiola with privately held Mission Pharmacal is a step in the right direction, but I'd much prefer to stick to the sidelines and wait for tangible late-stage evidence of success from its existing pipeline before even considering Retrophin a buy.