Silence's Breakthrough Drug May End Burdensome Bloodletting for Cancer Patients

LONDON, UK – August 10, 2026 – For thousands of people living with polycythemia vera (PV), a rare and chronic blood cancer, life is often dictated by the hematocrit number. Keeping this measure of red blood cells below a critical 45% threshold is a constant battle to prevent life-threatening blood clots, heart attacks, and strokes. The primary weapon in this fight has long been therapeutic phlebotomy—a modern form of bloodletting—a burdensome, repetitive procedure that drains not just blood, but energy and quality of life. Today, that paradigm may be on the cusp of a dramatic shift.

London-based Silence Therapeutics announced overwhelmingly positive results from a Phase 2 trial of its novel drug, divesiran. The data suggests that a simple, infrequent injection could effectively control the disease, potentially freeing patients from the relentless cycle of phlebotomy. For a community that has seen little therapeutic innovation targeting the root of their disease, this news represents more than just a clinical success; it’s a tangible beacon of hope.

Unpacking the SANRECO Trial: A Decisive Victory

The data comes from the SANRECO Phase 2 trial, a randomized, double-blind study involving 48 PV patients who were dependent on phlebotomy despite other treatments. The results, as one analyst noted, represent a “major catalyst” in the field. The trial’s primary goal was to see if divesiran could keep patients’ hematocrit below 45% without the need for phlebotomy between weeks 18 and 36. The outcome was nothing short of stunning.

A remarkable 88% of patients receiving divesiran met this primary endpoint, compared to just 19% of those on a placebo. The effect was robust across two different dosing schedules: 93.8% of patients receiving an injection every six weeks responded, as did an impressive 81.3% of those on a twelve-week (quarterly) schedule.

“Across the SANRECO Phase 1/2 program, divesiran has been well tolerated and has consistently delivered durable hematocrit control in phlebotomy-dependent patients with PV, regardless of risk level or disease severity,” said Dr. Marina Kremyanskaya, an Associate Professor of Medicine at the Icahn School of Medicine at Mount Sinai and a trial investigator. “These compelling results highlight divesiran’s potential to transform PV management with convenient, infrequent dosing that reliably controls hematocrit and addresses longstanding unmet needs for patients.”

The trial also met its key secondary endpoint, demonstrating a drastic reduction in the need for phlebotomies over the 36-week period. Patients on divesiran required an average of just 0.2 phlebotomies, while the placebo group needed 2.1. In fact, over 90% of patients on the drug required no phlebotomies at all. Furthermore, the treatment was found to be well-tolerated, with no new safety concerns arising.

The Science of Silence: A Precision Strike Against Disease

Divesiran represents a new frontier in medicine, leveraging a technology known as RNA interference (RNAi). Instead of introducing a chemical to block a biological process, these therapies work like a software patch for the body’s genetic code. They use short interfering RNA (siRNA) to find and “silence” a specific gene that is causing a disease.

In the case of PV, the disease is driven by the bone marrow’s uncontrolled overproduction of red blood cells. Divesiran targets a gene called TMPRSS6, which is expressed almost exclusively in the liver. This gene acts as a brake on a hormone called hepcidin, the body’s master regulator of iron. By silencing TMPRSS6, divesiran releases the brake, allowing hepcidin levels to rise. Higher hepcidin restricts the supply of iron to the bone marrow. Without this key ingredient, the overactive production of red blood cells slows to a manageable rate.

This precision-engineered approach is a far cry from the blunt instruments of phlebotomy or older cytoreductive drugs. It’s a first-in-class siRNA therapy for PV that addresses the underlying iron metabolism imbalance, a strategy that is gaining significant traction in the hematology community.

Beyond the Syringe: A New Horizon for Patients

To understand the impact of these results, one must understand the burden of living with PV. Beyond the constant threat of thrombosis, patients often suffer from debilitating symptoms like profound fatigue, cognitive fog, and intense itching (pruritus). The phlebotomies, while necessary for survival, create their own problems, often leading to iron deficiency that can worsen fatigue.

A treatment that not only controls hematocrit but also reduces these burdens could fundamentally alter the patient experience. The prospect of trading frequent clinic visits for a single, subcutaneous injection every three months is a monumental shift. The SANRECO trial data supports this, showing improvements in patient-reported outcomes as measured by the MPN-SAF Total Symptom Score.

“The unmet need in this patient population is significant,” commented one hematologist not involved with the study. “Current therapies often fall short or come with their own set of challenges. A well-tolerated therapy that provides durable hematocrit control with quarterly dosing would be a paradigm shift, dramatically improving convenience and quality of life.”

A Shot in the Arm for Silence Therapeutics

The market’s reaction to the news was immediate and decisive, with Silence Therapeutics’ stock (Nasdaq: SLN) surging by as much as 41% to a 52-week high. For the clinical-stage biotech, the success of divesiran, a wholly-owned asset, is a powerful de-risking event that validates its proprietary mRNAi GOLD™ platform.

The company now appears poised to challenge the existing treatment landscape, which is dominated by therapies like Incyte’s Jakafi (ruxolitinib), a JAK inhibitor approved for PV patients who don’t respond to first-line treatment. While effective for symptoms, it is not a cure. Divesiran’s unique mechanism and highly convenient dosing schedule could position it as a best-in-class therapy, particularly for the large population of patients dependent on phlebotomy.

“The SANRECO Phase 2 trial delivered our best-case outcome, confirming the impressive results observed in Phase 1 with dosing every six weeks and demonstrating equally robust and durable effects with quarterly dosing,” said Dr. Curtis Rambaran, Chief Medical Officer at Silence. “These results reinforce divesiran’s potential to become the first and best-in-class siRNA treatment for PV.”

With FDA Fast Track and Orphan Drug designations already secured, the path forward is becoming clearer. Silence Therapeutics plans to meet with regulators by the end of the year and aims to initiate a pivotal Phase 3 trial in the first half of 2027, focusing on the promising quarterly dosing regimen. If that trial succeeds, the company will be one step closer to bringing this transformative therapy to the patients who need it most.