"Today is all about not wanting to go home long," said Mike Antonelli on Friday, equity sales trader at R.W. Baird & Co., according to Marketwatch. In case that sounded confusing, Antonelli means that many investors didn't want to hold onto their stocks over the weekend, partly due to the uncertainty markets face this week as the "Brexit" scenario unfolds. A long-time-coming vote on whether or not the U.K. will leave the European Union is set for June 23.

Unfortunately, that Debbie-Downer analyst comment has a ring of truth to it, as the Dow Jones Industrial Average (DJINDICES: ^DJI) and the S&P 500 (SNPINDEX: ^GSPC) traded lower Friday, and ended down 1.06% and 1.19% for the week, respectively. Here's a look at some companies that made big moves and headlines.

Prepare for descent

Gettyimages Dv

Image source: Getty Images.

American Airlines Group Inc (NASDAQ:AAL) was one of the worst-performing stocks in the S&P 500 last week after it tumbled to a 20-month low. The 12% decline last week was due to a Wall Street analyst cutting the rating of the stock, and slashing its earnings estimates for the entire industry. This was, in part, due to recent terrorist attacks, higher fuel prices, and the aforementioned "Brexit" scenario.

More specifically, Bank of America Merrill Lynch analyst Andrew Didora cut American Airlines' stock rating to underperform, also known as a sell rating. He also cited the company's increasing debt load. Didora trimmed the entire industry's earnings-per-share estimates by 7% for the year, and 13% for 2017.

It certainly wasn't an optimistic note. His comments, combined with the fact that American Airlines is the world's largest airline, were enough to bring competing airlines down for the week. Delta Airlines ended nearly 10% lower, and Southwest Airlines dropped by more than 8%.

While the analyst note definitely makes some valid points -- especially if oil prices continue to climb -- consumers and travelers might be more resilient to recent terrorist attacks and the "Brexit" scenario than the market is giving the airlines credit for.

Clinical-stage woes

Outside of the airline sector, there was pain in other industries, too. Shareholders of clinical-stage biotech Infinity Pharmaceuticals (NASDAQ: INFI) were quick to jump ship after management reported disappointing results from a critical study. More specifically, the disappointing data from its Phase 2 monotherapy study of duvelisib, a possible treatment for non-Hodgkin lymphoma, failed to meet the response rate that Infinity and its collaboration partner, AbbVie, were hoping for.

Pharmacy

Image source: Getty Images.

Unfortunately, for investors hoping for a blockbuster, the stock price of Infinity was largely tied to the future success of duvelisib, and the stock price immediately plunged 70%. That leaves the remaining investors with a bleak outlook as the company is burning through nearly $40 million per quarter, and has just over $190 million in cash as of the most-recent quarter.

Another company with a similar song and dance this week was Revance Therapeutics (NASDAQ:RVNC), which reported that its clinical-stage treatment for crow's feet failed. Management hoped that, in the 450-patient trial, the product RT001 would show a two-point or greater improvement in crow's feet at 28 days post-treatment, or that it would deliver at least a one-point improvement in a patient assessment. RT001 failed on both counts.

Investors got hit with a substantial 27% decline for the week, which was less brutal than Infinity's soul-crushing 70% drop. Management expects the company has enough money on the books to get through 2017 and into 2018. That buys Revance a little time to invest in other products in its pipeline, and to try and drive investor enthusiasm and revenue.

Daniel Miller has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.