Silverback Therapeutics said late Thursday its initial public offering of stock raised gross proceeds of $241 million after the Seattle-based biotech upsized its planned share sale.

The shares jumped 35% when the stock opened for trading midday Friday, and closed at $25, up 19%.

Evidently responding to strong investor interest in its technology for targeting solid tumors, the company increased the size of an IPO that as recently as Nov. 30 was expected to raise about $152 million by selling 8 million shares at $19 each. The final offering sold 11.5 million shares at $21 apiece.

Under the ticker symbol “SBTX,” the shares began trading at $28.50 before settling into a range of $26.50-$27.50.

The company, led by president and CEO Laura Shawver, has a lead product candidate that is in Phase 1 trials for patients with advanced or metastatic HER2-expressing solid tumors.

Health care, including biotech, has been the strongest sector for new stock offerings in the past 12 months, accounting for 49% of IPO deals, according to Renaissance Capital.