After delivering a disappointing update on NKTR-214 in cancer patients this summer, Nektar Therapeutics' (NASDAQ: NKTR) shares have been struggling. The company didn't report any news today, so a negative report issued by Plainview LLC this month may be to blamed for its 17.2% tumble today.In February, Bristol-Myers Squibb (NYSE: BMY) inked a blockbuster deal to license rights to NKTR-214 following positive data last year for NKTR-214's use alongside Bristol-Myers' Opdivo.