The upgrade from Neutral to Outperform by a reputable analyst like Robert Driscoll, coupled with a significant increase in the price target from $3 to $8, suggests a strong bullish sentiment towards CytomX Therapeutics. This is likely based on positive developments within the company or promising prospects that have convinced the analyst of its improved performance potential. Such upgrades often lead to increased investor interest and can drive the stock price up in the short term.