Piper Jaffray analyst David Amsellem said his survey of 35 physicians indicated Insys Therapeutics' (INSY) sublingual spray form of fentanyl, Subsys, has room for further growth despite already having gained "significant" volume share. Specifically, the favorable feedback suggests further room for share gains at the expense of Teva's (TEVA) Actiq and Fentora, Amsellem tells investors in a research note. The analyst views the valuation of Insys shares as attractive given its growth potential. He reiterates an Overweight rating on the stock with a $48 price target.