Morgan Lieberman/Bloomberg via Getty Images(LOS ANGELES) -- Shares of PacWest Bancorp plunged more than 50% in early trading on Thursday, marking the latest spasm of financial distress after three of the nation's 30-largest banks fell within a matter of weeks. In all, PacWest stock has fallen more than 85% this year, erasing hundreds of millions of dollars in value. The Los Angeles-based midsized lender is exploring "all options" as it weighs offers from potential investors as well as the sale of a $2.7 billion loan portfolio, PacWest said in a statement on Wednesday. However, the c...