What Are Tagraxofusp's Common Non-CLS Side Effects in BPDCN?

While Capillary Leak Syndrome (CLS) is a well-known serious risk of tagraxofusp (Elzonris) therapy, it is not the only side effect you may experience. The most common non-CLS side effects include elevated liver enzymes, changes in blood counts, nausea, and fatigue ^[1][2]. Because tagraxofusp is given intravenously over five consecutive days in a 21-day cycle, your care team will closely monitor your blood work and vital signs before, during, and after these infusions to manage any side effects early ^[1][3]. In fact, your first cycle may require inpatient observation to ensure you are tolerating the medication well.

Increased Liver Enzymes (ALT/AST)

One of the most frequent side effects is an increase in liver enzymes on your blood tests, which can be a laboratory signal of possible liver-cell injury. In the main FDA-reviewed clinical study for BPDCN, approximately 64% of patients had increased ALT and 60% had increased AST (two key liver tests) at any severity grade ^[1].

A raised enzyme level is a laboratory finding, and many patients do not feel any physical symptoms when this happens ^[4]. While many of these enzyme spikes happen during the first treatment cycle and are temporary, they are not always minor ^[5]. Your medical team will monitor your liver blood tests (including ALT, AST, and bilirubin). If your levels rise too high, your doctor may investigate other causes, hold your dose, or adjust your treatment ^[3]. Never skip or stop doses on your own.

Drops in Blood Counts (Myelosuppression)

Treatment can also cause myelosuppression, a condition where your bone marrow produces fewer blood cells. For example, thrombocytopenia (low blood platelets, which help blood clot) of any grade was reported in about 49% of patients in the primary BPDCN study ^[1].

Because BPDCN itself crowds the bone marrow and lowers blood counts, the relationship between the drug and your blood levels is complex. In people whose marrow disease responds to treatment and clears the malignant BPDCN cells, blood counts may improve over time ^[6]. However, counts can also remain low or worsen due to the therapy itself. Your team will run a Complete Blood Count (CBC) to monitor your:

• Platelets: to check your risk for bleeding.
• Hemoglobin: to check for anemia.
• Absolute Neutrophil Count (ANC): a specific measure of white blood cells that indicates your risk for bacterial and fungal infections.

Depending on these numbers, your care team may recommend blood transfusions, growth-factor injections, or treatment delays to keep you safe ^[6][7].

Fatigue and Nausea

Fatigue (low energy, which can sometimes be severe) and nausea are very common side effects, each affecting at least 30% of patients receiving the standard dose of tagraxofusp ^[2].

• Fatigue: Feeling extremely tired is common, but you should not automatically assume it is just a harmless side effect of the drug. Fatigue can also be caused by anemia, infection, dehydration, or the underlying illness itself ^[6]. Tell your team if your fatigue suddenly worsens or interferes with basic daily activities. To manage standard fatigue, try pacing your activities and asking for help at home.
• Nausea: Anti-nausea medicines can be given before your treatment to prevent sickness, and you may be prescribed medication to take at home ^[7]. Eating small, frequent meals and staying hydrated can also help.

How Your Medical Team Monitors You

Managing these side effects relies on comprehensive monitoring before each dose and throughout your 21-day cycle ^[7]. Your care team will check your:

• Liver blood tests (AST, ALT, bilirubin) to watch for signs of liver injury.
• Complete Blood Count (CBC) to monitor for low platelets, anemia, and infection risk.
• Albumin levels, weight, and blood pressure to ensure you aren’t developing signs of Capillary Leak Syndrome ^[3][8].

Monitoring helps the team detect problems early, but labs cannot predict every reaction. It is vital to report new symptoms promptly.

When to Call Your Care Team Urgently

Do not wait for your next scheduled blood draw if you feel unwell. Seek emergency care or call your oncology team immediately (following your center’s specific after-hours instructions) if you experience:

• Fever (ask your team for their specific threshold, often 38.0°C / 100.4°F) or chills, which indicate a possible infection.
• Unusual bleeding, excessive bruising, or black/bloody stools.
• Severe dizziness, shortness of breath, or chest pain.
• Sudden weight gain or swelling, which are warning signs of Capillary Leak Syndrome ^[8].
• Jaundice (yellowing of the skin or eyes) or dark urine.
• Inability to keep fluids down or a severe drop in how often you urinate.