SanDisk tanked after cutting sales forecasts, making it the worst performer on both the S&P 500 and Nasdaq. The storage-chip manufacturer slashed sales estimates for its first quarter, citing lower than expected demand in its enterprise division and discounted prices. SanDisk expects revenue of $1.3 billion over the three months to March. That's down from previous guidance as high as $1.45 billion. This is the second disappointment in as many months. Two months ago, SanDisk's initial revenue guidance missed estimates of $1.6 billion. SanDisk shares plummeted nearly 20% to $66.20 on Thursday.