Image: Pandora Media.

The stock market has gone through a topsy-turvy quarter, and even though it's close to unchanged from the beginning of 2016, the volatility it has given investors has been a wake-up call to anyone who expected a smooth ride going forward. Monday's trading activity was relatively calm, with most major market benchmarks closing with only very modest moves. Even after the big bounce that stocks have seen over the past month, investors remain uncertain about key elements of future economic growth, and some individual stocks continue to be particularly troubling for investors. Among them are Valeant Pharmaceuticals (NYSE:BHC), Pandora Media (NYSE:P), and PJT Partners (NYSE:PJT), all of which posted substantial declines on Monday.

Valeant Pharmaceuticals fell 7% after the latest bad news to hit the drug company. On Monday, investors found out that outgoing CEO Michael Pearson had received a subpoena to testify at a hearing on April 27 before the Senate Special Committee on Aging in Washington, D.C. The committee has looked at a number of different situations involving high drug prices, and controversial pharmaceutical industry player Martin Shkreli is perhaps the best-known among those called before the panel. Pricing of prescription drugs has become a key issue in the current Presidential election, and Valeant has been at the epicenter of debate over pricing practices in the industry. With activist investor Bill Ackman taking a leadership role on Valeant's board, investors hope that the company will be able to weather the political storm and recover some of its lost ground in time.

Pandora Media dropped 12%, giving up all of its gains from Friday. The streaming-music specialist announced this morning that founder Tim Westergren would take over the reins as CEO at Pandora, positioning the move as a way "to accelerate the company's growth strategy." In Westergren's words, "We're on the cusp of realizing an extraordinary vision: fundamentally changing the way listeners discover and enjoy music and the way artists build and sustain their careers." Yet investors weren't happy that Pandora didn't explicitly address the reasons why departing CEO Brian McAndrews was leaving the company. Moreover, it's unclear how the strategic move will help Pandora be more competitive with its rivals in the industry, all of which share the pressures of maintaining profitability while spending enough to attract and retain customers.

Finally, PJT Partners finished the day down 11%. The advisory-focused investment bank saw its stock fall after a partner of the company was charged with criminal securities fraud and wire fraud offenses. The SEC also filed a civil action against Andrew Caspersen, who worked for PJT unit Park Hill Group. PJT Partners terminated Caspersen for cause, issuing a statement Monday afternoon that it had begun an internal investigation of the matter and "brought the matter to the attention of the U.S. Attorney's Office in Manhattan" as part of its cooperation with law enforcement officials. Nevertheless, with the lawsuits alleging losses of $95 million, investors are worried that insurance coverage and other resources that PJT Partners has to offset any liability might prove insufficient to prevent losses entirely.

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