U.S. stocks continued their three-day selloff at Thursday's midday trading. American Express (AXP) says it may have to cut jobs if the company cannot retain clients that could disappear as a result from losing its relationship with Costco (COST). The deal between American Express and Costco will expire next year. SanDisk (SNDK) tanked after lowering its Q1 revenue outlook. The memory chip maker warned weak demand and lower pricing for its guidance. Despite lowering its guidance, Lululemon (LULU) rose nearly 7% after beating earnings estimates. The yogawear retailer also showed an increase in same-store sales.