Response Genetics (RGDX) shares climbed in Monday’s pre-market session, after a late-Friday regulatory filing showed activist investor Becker Drapkin cut its stake last week in the developer of clinical diagnostic tests for cancer. RGDX was up 8.5% at $1.40 in recent pre-market trading, in a 52-week range of $1.09 to $2.93. The filing showed Becker…