What happened In an about-face from its impressive performance last week, Adaptimmune Therapeutics (NASDAQ: ADAP) stock declined by nearly 14% over the past five trading days. This occurred even though the cancer-focused biotech actually divulged some good news. So what That news was certainly encouraging. On Monday, Adaptimmune said that its phase 1 SURPASS trial gauging the efficacy of its ADP-A2M4CD8 SPEAR T-cell therapy to reduce certain types of solid tumors showed a response rate of 36% and a disease control rate of 86%. One patient with ovarian cancer recorded a complete response to the therapy. Image source: Getty Images. "It is no longer a question of whether our SPEAR T-cells are effective against a range of MAGE-A4 expressing tumors -- they undoubtedly are," Adaptimmune quoted CEO Adrian Rawcliffe as saying. "Now, our focus is on turning them into approved therapies." That's an exciting prospect, but the update couldn't compete with the Sept. 7 announcement that the company had signed a licensing and partnership deal with Genentech (now owned by deep-pocketed international pharmaceutical company Roche). The total value of the deal could top a mouth-watering $3 billion for Adaptimmune when potential milestone payments and royalties are included. Now what It seems that numerous investors engaged in profit-taking with their Adaptimmune positions after considering last weekend whether they wanted to sell or hold. This would explain the general five-day slide in the stock price, despite Monday's good news. But the best returns from investing, particularly in the biotech sector, are rewarded with patience. The fight against cancer is going to be a long and difficult one. Adaptimmune is well equipped for the battle, so investors shouldn't be discouraged by this week's weakness. 10 stocks we like better than Adaptimmune TherapeuticsWhen our award-winning analyst team has a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* They just revealed what they believe are the ten best stocks for investors to buy right now... and Adaptimmune Therapeutics wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of September 17, 2021 Eric Volkman has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.Source