With those caveats in mind, Perceptive Advisors was the largest buyer of Sarepta in the third quarter, adding 1.4 million shares. Wellington Management also bought 1 million shares.

BlackRock was a notable (perhaps regretful) Sarepta seller, shedding 8.5 million shares across two different entities, according to Whale Wisdom.

For Arena Pharmaceuticals ( ARNA), three new buyers of note during the third quarter, which began right before the approval of the company's weight-loss pill Belviq: Deerfield Management (7.8 million shares), Capital World Investors (5 million shares) and QVT Financial (2.7 million shares)

Blackrock sold 9.9 million Arena shares during the third quarter. There was also significant net-selling options activity in Arena from Susequehanna International, Barclays, Group One Trading and Citigroup, according to Whale Wisdom.

Spectrum Pharmaceuticals ( SPPI) lost Tang Capital as a major shareholder in the third quarter. The San Diego-based hedge fund sold 4 million Spectrum shares, retaining 1.5 million shares.

-- Reported by Adam Feuerstein in Boston.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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