Piper Jaffray analyst Sean Wieland reiterates an Underweight rating on MedAssets (MDAS) after Starboard Value last night disclosed an 8.7% stake in the company and assumed an activist role. Shares of the healthcare servicer rallied $2.96 to $26.56 following news of Starboard's stake. MedAssets' issues are structural, and it will be a challenge to find operating expense savings of $60M-$90M without impacting revenue or growth, Wieland tells investors in a research note. Further, one cannot compare EBITDA margins between MedAssets and Premier (PINC), as the latter company has a unique corporate tax structure and a more service-intensive business model, the analyst writes. Wieland keeps a $15 price target for shares of MedAssets.