Arrowhead Pharmaceuticals, Inc. (NASDAQ:ARWR) presented detailed results from the randomized, double-blind, placebo-controlled Phase 3 SHASTA-3 and SHASTA-4 studies in 757 adults with severe hypertriglyceridemia. Four quarterly 25-mg doses of plozasiran produced median triglyceride reductions of 79% and 81% at Month 12, compared with approximately 27% for placebo in each study.
A prespecified pooled analysis showed a 78% reduction in the rate of all acute-pancreatitis events, with a rate ratio of 0.22 and a 95% confidence interval of 0.07 to 0.67. However, that result represented a 4.1% absolute risk reduction and a one-year number needed to treat of 24. Arrowhead Pharmaceuticals, Inc. plans to submit a supplemental New Drug Application for the broader severe-hypertriglyceridemia population before the end of 2026 and use a Priority Review Voucher. Plozasiran, marketed as REDEMPLO, is FDA-approved as an adjunct to diet to reduce triglycerides in adults with familial chylomicronemia syndrome.
Bull Case
Arrowhead Pharmaceuticals, Inc. demonstrated that triglyceride lowering was both deep and consistent across two pivotal studies. At Month 12, 91% and 93% of plozasiran-treated patients in SHASTA-3 and SHASTA-4, respectively, moved below the 500 mg/dL threshold associated with pancreatitis risk. Only 51% and 50% of placebo recipients reached that level. More than half of treated patients also reached triglycerides below 150 mg/dL.
Across the full pooled population, plozasiran reduced the risk of a first pancreatitis event, with a hazard ratio of 0.26. The clinical benefit was substantially larger among patients with previous acute pancreatitis. In that subgroup, plozasiran reduced the event rate by 91%, with a 34% absolute risk reduction and a one-year number needed to treat of approximately three. That subgroup result gives Arrowhead Pharmaceuticals, Inc. a strong case for expanding treatment beyond the rare familial-chylomicronemia population.
Overall treatment-emergent adverse events occurred in 73% of both treatment groups, while serious events occurred in 8.3% of plozasiran recipients and 10% of placebo recipients. No clinically meaningful liver-enzyme or platelet changes emerged. In a prespecified MRI-PDFF substudy, there was no statistically significant treatment-emergent increase in hepatic fat fraction.
Bear Case
The broad-population result is less striking in absolute terms. Treating 24 patients for one year to prevent one pancreatitis event may support use in selected patients, but the benefit-risk and reimbursement arguments are less clear for patients without previous pancreatitis. The primary endpoint in each study was triglyceride reduction, while the pancreatitis evidence came from a prespecified pooled event analysis rather than a standalone outcomes trial.
Metabolic safety also requires attention. Arrowhead Pharmaceuticals, Inc. reported worsening-glycemic-control adverse events in 14.3% of plozasiran recipients and 8.7% of placebo recipients. Mean HbA1c showed only minimal to modest absolute changes without worsening over time, but the adverse-event imbalance could matter in a population with substantial metabolic risk. Three deaths occurred among treated patients, and all three were assessed as unrelated to treatment and attributed to pre-existing disease.
Hedge Fund Data
The filings available so far reflect positions held before Arrowhead Pharmaceuticals, Inc. reported pooled Phase 3 SHASTA-3 and SHASTA-4 results. Insider Monkey’s database showed 58 hedge funds holding Arrowhead Pharmaceuticals, Inc. at the end of 2Q2026, up from 53 funds three months earlier.
Conclusion
The results support a broader-label filing for Arrowhead Pharmaceuticals, Inc., but the clinical case is not equally strong across the full population. The 34% absolute reduction among patients with previous pancreatitis is compelling, while the 4.1% reduction across all participants is more modest. Approval and commercial adoption will depend on the FDA’s interpretation of the pooled pancreatitis analysis and the glycemic-safety imbalance.
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This article is originally published at Insider Monkey.
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