Pazopanib: What It Is, Uses, and Potential Side Effects

Pazopanib is an oral cancer drug that works by starving tumors of their blood supply, and it carries two main regulatory approvals: advanced kidney cancer and certain soft tissue sarcomas. Sold under the brand name Votrient, it belongs to a class of targeted therapies that block the growth of new blood vessels tumors need to survive. The drug is effective enough that it has become a standard option in both diseases, but its side-effect profile, particularly liver toxicity and high blood pressure, demands close monitoring throughout treatment.

How Pazopanib Works

Tumors need a constant supply of blood to grow, and they recruit that supply by sending chemical signals that trigger the formation of new blood vessels, a process called angiogenesis. Pazopanib interferes with this process by blocking the activity of several receptor proteins on the surface of cells that respond to those signals. Its primary targets are the receptors for vascular endothelial growth factor (VEGF receptors 1, 2, and 3) and platelet-derived growth factor (PDGF receptors alpha and beta), along with a receptor called c-Kit.¹ By blocking these receptors, pazopanib prevents the internal signaling cascade that tells cells to build new blood vessels. Without fresh blood supply, the tumor’s growth slows or stalls.²

This mechanism makes pazopanib part of the broader family of tyrosine kinase inhibitors, drugs that work inside the cell rather than on the cell surface. It is taken once daily as a tablet, which makes it more convenient than intravenous chemotherapy, though it comes with its own set of practical requirements around food timing and drug interactions.

Kidney Cancer

Pazopanib’s first and most established use is in advanced or metastatic renal cell carcinoma, the most common type of kidney cancer. A landmark phase III trial compared pazopanib to placebo and found that the drug more than doubled the time before the cancer progressed: patients on pazopanib had a median progression-free survival of about 9.2 months, compared with 4.2 months on placebo.³ That benefit held across different patient groups. People who had never received prior treatment did even better, with a median progression-free survival of about 11 months, while those who had already tried an older immune-based therapy still gained roughly three extra months before their disease worsened.³

A natural question is how pazopanib stacks up against sunitinib (Sutent), the other widely used drug in the same class. A head-to-head trial published in the New England Journal of Medicine found that the two drugs produced similar outcomes: pazopanib was noninferior to sunitinib for progression-free survival, and overall survival was essentially the same between the two groups.⁴ Where they differed was in tolerability. Sunitinib caused more fatigue, more hand-foot syndrome (painful blistering on the palms and soles), and more drops in platelet counts. Pazopanib, on the other hand, was more likely to cause liver enzyme elevations. On quality-of-life surveys, pazopanib came out ahead in 11 of 14 measured domains, particularly in areas related to fatigue and mouth or hand soreness.⁴ For many patients and oncologists, that quality-of-life advantage tips the decision toward pazopanib when the two drugs are otherwise roughly equivalent in effectiveness.

Soft Tissue Sarcoma

Pazopanib’s second approved use is for advanced soft tissue sarcoma, a diverse group of cancers that arise from muscles, fat, blood vessels, nerves, and other connective tissues. The pivotal trial here, known as PALETTE, enrolled patients whose sarcomas had already progressed on standard chemotherapy. Pazopanib extended median progression-free survival to about 4.6 months, compared with 1.6 months on placebo.⁵ That three-month gain may sound modest in absolute terms, but for patients with advanced sarcoma who have run out of chemotherapy options, it represents a meaningful delay in disease progression.

One important limitation: the PALETTE trial excluded certain sarcoma subtypes, particularly those arising from fat tissue (adipocytic sarcomas like liposarcoma). The drug is specifically approved for non-adipocytic soft tissue sarcomas, so it is not a blanket sarcoma treatment. Subgroup analyses from the trial have confirmed that pazopanib’s activity holds across most of the eligible sarcoma subtypes, though responses vary.⁶

Liver Toxicity

The side effect that gets the most clinical attention with pazopanib is liver damage. Elevations in liver enzymes, particularly alanine aminotransferase (ALT), are common and sometimes severe. In the head-to-head trial against sunitinib, about 60% of pazopanib-treated patients had ALT increases.⁴ A real-world study tracking 133 patients found that roughly one in five developed clinically meaningful liver toxicity during treatment.⁷

The good news is that liver toxicity is usually manageable. In that same real-world study, of the 25 patients who developed liver problems, only seven had to stop pazopanib permanently. The remaining 18 were able to continue or restart the drug, and half of those patients stayed on their original dose for the rest of their treatment.⁷ That said, routine liver function blood tests are essential, particularly in the first few months. If enzyme levels spike, treatment may need to be paused or the dose reduced until things settle.

High Blood Pressure

Hypertension is one of the most common side effects of all drugs that block VEGF signaling, and pazopanib is no exception. In one study that carefully tracked blood pressure, 57% of patients developed treatment-related hypertension, with a typical onset within roughly the first month of therapy. The median peak systolic blood pressure during treatment was about 168 mmHg, well above normal.⁸ Even patients who had normal blood pressure before starting pazopanib were at risk: 43% of previously normotensive patients developed new-onset hypertension.⁸

The underlying mechanism likely involves disruption of nitric oxide signaling. Research in kidney cancer patients showed that pazopanib treatment was associated with decreased levels of nitric oxide metabolites in both urine and blood, alongside increased protein in the urine.⁹ Nitric oxide is a key molecule that keeps blood vessels relaxed, so when its levels drop, blood vessels constrict and pressure rises.

There is an intriguing flip side to this problem. A study of over 300 kidney cancer patients treated with either pazopanib or sunitinib found that those who developed treatment-related hypertension actually lived longer. Patients with drug-induced high blood pressure had a median progression-free survival of about 15.6 months, compared with 6.4 months for those who did not develop hypertension. Overall survival followed the same pattern, at roughly 35 months versus 14 months.¹⁰ This suggests that hypertension may be a sign the drug is hitting its target hard, essentially a marker that the anti-angiogenic effect is working. That does not mean hypertension should go untreated, but it can be somewhat reassuring when blood pressure readings start climbing.

Other Cardiovascular Concerns

Beyond hypertension, pazopanib and related drugs have been linked to QT interval prolongation, a change in heart rhythm that can occasionally lead to dangerous arrhythmias, as well as other cardiovascular events.¹¹ These cardiac effects are less common than hypertension but serious enough that patients typically get baseline heart function assessments before starting treatment. People with pre-existing heart conditions need especially close follow-up. Oncologists generally monitor ECGs periodically, and electrolyte levels (particularly potassium and magnesium) are kept in check because imbalances can worsen heart rhythm issues.

Digestive Side Effects and Hair Changes

Gastrointestinal complaints are among the most frequently reported side effects. Nausea, diarrhea, and vomiting showed up in early clinical trials and remain consistent findings in real-world practice.¹² Fatigue is also very common. Most of these symptoms are mild to moderate, but they can wear patients down over months of daily treatment. Adjusting meal timing, staying well-hydrated, and using anti-nausea medications proactively can help.

A less expected but visually striking side effect is hair depigmentation. Patients sometimes notice their hair gradually turning lighter, shifting from darker shades toward white or blond over weeks to months. In rare cases, the change can be dramatic and sudden. One published case report described a patient whose hair and eyebrows depigmented virtually overnight after only a few weeks of therapy.¹³ This happens because pazopanib inhibits the c-Kit receptor, which plays a role in melanin production. The effect is usually cosmetic and reversible once the drug is stopped, but it can be alarming if patients are not warned about it.

Why Food and Stomach Acid Matter

Pazopanib has some unusual dosing requirements. The standard dose is 800 mg taken once daily on an empty stomach, at least one hour before or two hours after eating. Food substantially increases how much drug gets absorbed, which raises the risk of side effects in unpredictable ways. However, research from the DIET study found that a lower dose of 600 mg taken with food produced equivalent drug exposure to the standard 800 mg fasted dose, and patients preferred taking it with a meal.¹⁴ This option may be discussed with an oncologist, particularly for patients who struggle with the fasting requirement or experience nausea on an empty stomach.

Stomach acid levels also affect how well pazopanib dissolves and gets absorbed. Proton pump inhibitors, the widely prescribed heartburn drugs like omeprazole and esomeprazole, raise stomach pH and can dramatically reduce pazopanib absorption. One pharmacokinetic study showed that taking esomeprazole alongside pazopanib decreased the drug’s blood levels by about 40%.¹⁵ That is a large enough drop to potentially make the cancer treatment less effective. Guidelines recommend avoiding proton pump inhibitors during pazopanib therapy altogether, or at least using alternative acid-reducing strategies that do not raise pH at the time of pazopanib dosing.¹⁶ This is something patients should flag with their care team, since proton pump inhibitors are among the most commonly prescribed medications and many people take them without thinking twice.

Other Drug Interactions

Pazopanib is broken down in the liver primarily by an enzyme called CYP3A4, which also metabolizes a long list of other drugs. Anything that strongly inhibits this enzyme can cause pazopanib levels to rise sharply. The antifungal drug ketoconazole, a potent CYP3A4 inhibitor, boosted pazopanib blood levels by about 66% when the two were taken together.¹⁷ On the flip side, drugs that ramp up CYP3A4 activity, such as the anti-seizure medications carbamazepine and phenytoin, can reduce pazopanib levels by roughly 30 to 50%, potentially making it less effective.¹⁷

The practical takeaway is that patients starting pazopanib should bring a complete list of all medications, supplements, and over-the-counter drugs to every oncology appointment. Even common items like grapefruit juice (a CYP3A4 inhibitor) and St. John’s wort (a CYP3A4 inducer) can shift drug levels meaningfully. Therapeutic drug monitoring, where blood samples are taken to check pazopanib concentrations directly, is used at some centers to fine-tune dosing.

Combining Pazopanib With Immunotherapy

One of the most active areas of research involves pairing pazopanib with immune checkpoint inhibitors, drugs that help the immune system recognize and attack cancer cells. The rationale makes biological sense: blocking tumor blood supply with pazopanib may alter the tumor’s local environment in ways that make it more vulnerable to immune attack. Several early-phase trials have explored these combinations.

In soft tissue sarcoma, a phase II trial tested pazopanib alongside durvalumab, a drug that blocks the PD-L1 protein tumors use to hide from the immune system.¹⁸ In kidney cancer, combinations with pembrolizumab and nivolumab have also been studied.^{19 20} These combinations are still largely experimental, and the safety picture gets more complicated when two powerful drugs are layered together. Liver toxicity, in particular, can be amplified. For now, these combinations are not standard treatment outside clinical trials, but they represent a plausible direction for the future.

Why Some Patients Stop Responding

Like most targeted cancer therapies, pazopanib does not work forever. Tumors eventually develop resistance, and researchers are working to understand why. Laboratory work on tumor cell lines that became resistant to pazopanib found that the changes were relatively focused: only about 6% of the cells’ protein signaling landscape was altered in the process of becoming resistant. The resistant cells showed increased activity in pathways that regulate cell structure and movement, suggesting the tumor may be finding alternative ways to sustain itself and spread.²¹ Understanding these escape routes could eventually lead to strategies for overcoming or delaying resistance, though that work is still in early stages.

Predicting Who Will Benefit

Not every patient responds to pazopanib equally, and the search for biomarkers that can predict who will benefit most is an active research priority, especially in sarcoma. One approach has looked at gene expression patterns in tumor tissue. A scoring system based on the combined activity of three genes (NTRK3, IGF1R, and KDR) was found to distinguish sarcoma patients likely to have good, intermediate, or poor outcomes on pazopanib.²² Other researchers have investigated whether specific gene alterations or immune-related proteins in tumor samples might serve as predictive markers.^{23 24}

None of these biomarker tools are yet used routinely in clinical decision-making. They need larger, prospective studies before they can guide treatment choices. But the concept is promising: rather than prescribing pazopanib to all eligible patients and seeing who responds, future practice could involve analyzing a biopsy sample upfront and selecting the patients most likely to benefit.

Use in Children and Adolescents

Pazopanib is approved for adults, but pediatric oncologists have explored its use in children with hard-to-treat sarcomas and other solid tumors. A phase I study conducted by the Children’s Oncology Group established dosing and pharmacokinetic data in younger patients.²⁵ Since then, retrospective institutional reports and multicenter real-world studies have documented pazopanib being used off-label in pediatric patients, sometimes alone and sometimes combined with other drugs like topotecan.^{26 27}

The evidence here is limited to small retrospective studies rather than large randomized trials, so pediatric use of pazopanib remains off-label and typically reserved for situations where standard treatments have failed. Children’s bodies process drugs differently than adults’, and the long-term effects of blocking angiogenesis in a still-developing body raise additional concerns. Bone growth, wound healing, and organ development all depend on healthy blood vessel formation, so the risk-benefit calculation is more complicated in younger patients. Still, for children with aggressive sarcomas and few remaining options, pazopanib offers at least a potential path forward.