Shares of Castle Biosciences (NASDAQ: CSTL) were down more than 20.2% for the week as of Thursday's close, according to data provided by S&P Global Market Intelligence. The healthcare stock closed last week at $20.30, then fell to as low as $15.55 on Wednesday. Castle stock is down by more than 31% this year. The company markets six tests designed to address treatment plan options in dermatologic cancers, uveal melanoma, Barrett's esophagus, and mental health conditions.

On Tuesday, the medical diagnostics company reported Securities and Exchange Commission (SEC) filings that showed on July 7 that CEO and President Derek Maetzold sold 25,116 shares of Castle stock for more than $500,000 while Chairman of the Board Daniel Bradbury sold 50,000 shares for just over $1 million. Insider sales, while often done for reasons that have little to do with the health of the company, commonly send share prices lower, particularly when they involve upper management.

These insider sales were a good example of selling for profits on good news. The company's stock rose 33% on July 7 when it announced new data on its DecisionDX-SCC test, a gene expression profile risk-stratification test for patients with squamous cell carcinoma, that showed improved risk prediction.

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Source Fool.com