Shares of Genprex Inc. GNPX, +167.18% skyrocketed 121% on massive volume in afternoon trading Monday, after the gene therapy company said its Reqorsa Immunogene Therapy was granted Fast Track Designation (FTD) by the U.S. Food and Drug Administration for use in combination with Merck & Co. Inc.’s MRK, +0.30% cancer treatment Keytruda. Trading volume exploded to 163.9 million shares, compared with the full-day average of about 476,600 shares, and enough to make the stock the most actively traded on major U.S. exchanges. The company said the FTD is for use in patients with histologically confirmed unresectable stage III or IV non-small cell lung cancer (NSCLC) whose disease progressed after treatment with Keytruda. “This Fast Track Designation is an important step in our efforts to accelerate clinical development of REQORSA and another validation of the potential of REQORSA to treat the unmet medical need of patients with late-stage NSCLC,” said Genprex Chief Executive Rodney Varner. The stock, which closed at a near two-year low of $1.21 as recently as Dec. 29, has now gained 7.0% over the past three months, while the iShares Biotechnology ETF IBB, -0.16% has lost 4.6% and the S&P 500 SPX, +0.64% has advanced 9.9%.