What Is Sunitinib and How Is It Used to Treat Cancer?

Sunitinib (sold under the brand name Sutent) is an oral cancer drug that works by blocking several proteins tumors rely on to grow and build their own blood supply. Approved by the FDA in 2006, it became one of the first so-called “targeted therapies” to treat multiple cancer types with a single pill, and it remains a standard option for advanced kidney cancer, certain gastrointestinal tumors, and rare pancreatic tumors. The drug’s story is more layered than a simple approval date suggests, though, because newer immunotherapy combinations have reshaped where sunitinib fits in treatment plans and researchers continue to learn why some patients respond dramatically while others see little benefit.

How Sunitinib Attacks Cancer

Most traditional chemotherapy drugs kill any rapidly dividing cell in the body, cancerous or not. Sunitinib takes a different approach. It is classified as a multitargeted receptor tyrosine kinase inhibitor, which in plain terms means it plugs into specific docking sites on the surface of cells and blocks the chemical signals those docking sites normally relay. The targets it blocks include receptors for vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF), both of which tumors hijack to recruit new blood vessels and feed their growth.¹ By choking off that blood supply, sunitinib starves the tumor.

But the drug does more than cut off blood vessels. It also blocks KIT (the stem cell factor receptor), FLT3, RET, and CSF1R, among others.² Some of these are proteins that cancer cells themselves depend on to survive and multiply. KIT, for instance, is mutated and constantly switched on in most gastrointestinal stromal tumors, which is exactly why sunitinib works against them. This dual strategy of attacking both the tumor’s blood supply and the tumor’s own growth signals is what earned sunitinib the label “multitargeted” and made it useful across several cancer types.³

The Cancers Sunitinib Treats

Sunitinib has regulatory approval for three main cancer types, and occasionally sees use in others through clinical trials or off-label prescribing.

Advanced Kidney Cancer

Kidney cancer, specifically the clear-cell subtype of renal cell carcinoma (RCC), is where sunitinib made its biggest mark. In a landmark trial comparing sunitinib to interferon alfa (the previous standard), patients on sunitinib went roughly eleven months before their disease worsened, compared to five months on interferon. The response rate was also dramatically higher: about 31% of sunitinib patients saw their tumors shrink measurably, versus 6% on interferon.⁴ Earlier studies in patients who had already failed interferon therapy confirmed the drug’s activity in that setting as well, with about a third of patients responding and a median of just over eight months before progression.⁵

For years, sunitinib was the default first-line treatment for advanced RCC. That has changed considerably with the arrival of immunotherapy-based combinations, a shift covered in more detail later in this article.

Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are rare cancers of the digestive tract driven largely by mutant KIT or PDGFR proteins. The first-line drug for GISTs is imatinib (Gleevec), which targets many of the same kinases. When imatinib stops working or patients cannot tolerate it, sunitinib steps in as the standard second-line option.⁶ The specific mutations in a patient’s tumor influence how well sunitinib works here. Tumors with certain KIT exon 9 mutations, for example, tend to respond differently than those with exon 11 mutations, making genetic testing of the tumor an important part of treatment planning.

Pancreatic Neuroendocrine Tumors

Pancreatic neuroendocrine tumors (pNETs) are uncommon growths arising from hormone-producing cells in the pancreas. In a placebo-controlled trial, sunitinib more than doubled progression-free survival: roughly eleven months versus five and a half months. Perhaps more striking, deaths were cut by more than half during the study period, with 10% of sunitinib patients dying compared to 25% on placebo.⁷ A later updated analysis confirmed the doubling of progression-free survival. The overall survival improvement was close to ten months, though the difference did not reach formal statistical significance, likely because many patients originally assigned to placebo crossed over to sunitinib when the early results became clear.⁸

How Sunitinib Is Taken

Sunitinib comes as a capsule swallowed once a day with or without food. The most common schedule is the “4/2” regimen: 50 mg daily for four weeks, followed by two weeks off. That two-week break gives the body time to recover from side effects before the next cycle starts.⁹

Researchers have tested alternatives. A continuous daily dose of 37.5 mg, without any off-weeks, was compared head-to-head with the 4/2 schedule in a randomized trial. The continuous schedule did not offer better tumor control and was not easier to tolerate; in fact, the 4/2 schedule was better at delaying the combination of death, progression, and worsening symptoms.¹⁰ Another modified schedule, two weeks on and one week off (the “2/1” schedule), has gained traction in clinical practice. In one study, patients on 2/1 needed significantly fewer dose interruptions due to side effects (27% versus 53%) and achieved comparable or even longer progression-free survival, though neither difference reached statistical significance.¹¹ Many oncologists now use 2/1 in practice for patients who struggle with side effects on the standard schedule.

One practical consideration worth knowing: sunitinib is processed in the liver by an enzyme called CYP3A4, and drugs that strongly speed up or slow down that enzyme can significantly alter how much sunitinib is actually active in the body. In a study of HIV-positive cancer patients, the anti-HIV drug ritonavir (a potent inhibitor of CYP3A4) decreased levels of sunitinib’s active metabolite, while efavirenz (which revs up CYP3A4) increased it.¹² This means anyone on sunitinib needs to be upfront with their oncologist about every other medication they take, including over-the-counter supplements and even grapefruit juice, which also inhibits CYP3A4.

Side Effects to Expect

Sunitinib is generally better tolerated than traditional chemotherapy, but it carries its own distinct set of side effects. Understanding these helps patients recognize what is normal, what needs medical attention, and what might lead to a dose adjustment.

Skin, Hair, and Nail Changes

Skin reactions are among the most visible side effects. In a pooled analysis, about 19% of patients developed hand-foot skin reaction (painful redness, swelling, or blistering on the palms and soles), and roughly 28% noticed skin discoloration, often a yellowish tint caused by the drug’s own color. Hair color changes affected about 10% of patients, sometimes appearing as alternating bands of pigmented and depigmented hair that track the on-off treatment cycles. Dry skin, rash, and mild hair thinning also occurred, though severe forms of any of these were uncommon.¹³ The hand-foot reaction seen with sunitinib is a different entity from the hand-foot syndrome caused by older chemotherapy drugs like capecitabine; it tends to affect pressure-bearing areas of the hands and feet and is managed differently.¹⁴

Cardiovascular Effects

Heart-related side effects deserve particular attention. In an early clinical study, about 47% of patients on sunitinib developed high blood pressure, and roughly 11% experienced a cardiovascular event such as heart failure. When researchers looked specifically at heart pumping function, about 28% of patients at the approved dose had a meaningful drop.¹⁵ A larger multicenter analysis confirmed the pattern: close to 19% of patients developed some degree of cardiac abnormality, and about 7% had grade 3 heart dysfunction or heart failure. Blood pressure problems often showed up after the third cycle of treatment.¹⁶ The good news is that heart dysfunction generally improved when sunitinib was paused and standard cardiac medications were started. Oncologists typically monitor blood pressure at every visit and check heart function periodically during treatment.

Thyroid Dysfunction

An underactive thyroid is surprisingly common with sunitinib. In one study, 44% of patients on sunitinib developed hypothyroidism.¹⁷ The mechanism is not fully settled. Some evidence points to a destructive process in the thyroid gland itself, potentially triggered by the drug’s effect on blood vessels feeding the thyroid. Patients sometimes go through a brief phase of overactive thyroid (from the damaged gland releasing stored hormone) before tipping into hypothyroidism. Thyroid function tests are routinely checked during sunitinib treatment, and standard thyroid hormone replacement corrects the problem without requiring a change in cancer therapy.

Fatigue and Overall Quality of Life

Fatigue is probably the side effect patients notice most in daily life. In a detailed analysis of kidney cancer patients, fatigue was worst during the first cycle of sunitinib, then stabilized. Over subsequent cycles, patients did not report statistically significant worsening of fatigue. Even more reassuring, when fatigue levels were matched grade-for-grade against patients on interferon, quality-of-life scores were consistently better with sunitinib.¹⁸ In patients with pancreatic neuroendocrine tumors, quality-of-life questionnaires showed essentially no difference between sunitinib and placebo across most domains, except for diarrhea, a recognized and manageable side effect.¹⁹ The overall picture is that sunitinib extends disease control without substantially worsening how patients feel day-to-day, once they get past the first treatment cycle.

Where Sunitinib Fits Now That Immunotherapy Has Arrived

The treatment landscape for advanced kidney cancer has shifted dramatically since sunitinib’s approval. Combinations pairing an immune checkpoint inhibitor with either another checkpoint inhibitor or a newer tyrosine kinase inhibitor have, in multiple large trials, overtaken sunitinib as the preferred first-line option for most patients. The question of exactly how sunitinib compares to these newer regimens, however, depends on the patient’s risk profile.

For patients classified as intermediate or poor risk, immunotherapy combinations clearly outperform sunitinib in overall survival. But for favorable-risk patients, those with slower-growing disease, the picture is muddier. A meta-analysis of randomized trials found that immunotherapy-plus-TKI combinations improved progression-free survival compared to sunitinib in favorable-risk patients, but did not produce a statistically significant improvement in overall survival.²⁰ A separate meta-analysis similarly found that while combination therapy produced higher response rates and more complete responses, neither overall survival nor progression-free survival differences reached statistical significance in favorable-risk patients when all types of immunotherapy combinations were pooled together.²¹

This means sunitinib is no longer the automatic first choice for most kidney cancer patients, but it has not disappeared either. In favorable-risk disease, where immunotherapy’s survival advantage is uncertain, sunitinib remains a reasonable option, and some oncologists prefer it for patients who want to avoid the autoimmune side effects that checkpoint inhibitors sometimes trigger. It also remains the standard of care for GISTs after imatinib failure and for pancreatic neuroendocrine tumors, where immunotherapy combinations have not displaced it.

Why Sunitinib Stops Working

Nearly all patients who initially respond to sunitinib eventually develop resistance, a frustrating reality shared by most targeted cancer therapies. Tumors can adapt in several ways. They can activate alternative signaling pathways that bypass the receptors sunitinib blocks. They can develop new mutations in the very targets sunitinib inhibits, changing the shape of the docking site so the drug no longer fits well.

One particularly inventive mechanism involves the cell’s own recycling system. Cancer cells can trap sunitinib inside compartments called lysosomes, acidic pouches normally used to break down cellular waste. Because sunitinib is a weak base, it gets drawn into these acidic compartments and locked away, unable to reach the signaling proteins it is supposed to inhibit. Researchers found that resistant cells accumulated up to 2.5 times more sunitinib than sensitive cells, yet the drug had no effect on key growth signals because it was stuck in the wrong part of the cell.²² Further work showed that the number of lysosomes in a cell actually predicts how resistant it will be: more lysosomes means more trapping and less drug reaching its targets.²³ This lysosomal trapping is not unique to sunitinib; other drugs with similar chemical properties face the same fate, making it a broader challenge for drug development.

Predicting Who Will Respond

One of the biggest open questions in oncology is figuring out which patients will benefit from a given drug before starting treatment. For sunitinib, most decisions currently rely on clinical risk scores rather than molecular tests. But researchers are working to change that.

At a basic level, tumors with high expression of VEGF, the growth factor most central to sunitinib’s mechanism, appear to respond better. One study found that significantly higher VEGF levels in tumor tissue, compared to healthy kidney tissue, predicted a better response to the drug.²⁴ That makes intuitive sense: if the tumor is heavily dependent on VEGF-driven blood supply, blocking VEGF receptors should hurt it more.

More sophisticated approaches are emerging. One group analyzed the protein and phosphoprotein profiles of kidney cancer tumors from 26 patients and identified a 78-marker signature that distinguished sunitinib-resistant tumors from sensitive ones. Resistant tumors showed higher activity in certain translation-related proteins, while sensitive tumors had more active MAPK and EGFR signaling, pathways that intersect with the targets sunitinib blocks.²⁵ These findings are still early-stage and too complex for routine clinical use, but they point toward a future where a biopsy could help predict whether sunitinib is the right drug before the first dose is swallowed.

Kinase activity profiling is another experimental approach, with researchers suggesting that measuring the actual enzymatic activity in a tumor sample, rather than just what genes are turned on, could help predict not only who will respond but also who is likely to experience serious side effects.²⁶ None of these biomarker strategies have been validated in large prospective trials yet, so for now, treatment decisions still rest on tumor type, clinical risk factors, and individual patient circumstances. The science is moving in the right direction, but the clinical tools are not quite there.

Sunitinib and Drug Interactions

Beyond the CYP3A4 interactions mentioned earlier, sunitinib itself can interfere with other medications through a separate mechanism. It blocks certain transport proteins, known as P-glycoprotein and ABCG2, that sit on cell membranes and pump drugs out of cells.²⁷ These transporters normally limit how much of certain medications gets absorbed from the gut or enters the brain. By blocking them, sunitinib can increase blood levels of drugs that rely on these pumps for clearance. This is one reason oncologists carefully review every medication a patient takes and why patients should always report new prescriptions, supplements, or herbal remedies to their treatment team.

Sunitinib’s reactive metabolites also warrant mention. When the liver processes sunitinib, it produces aldehyde intermediates that are chemically reactive and can bind to liver enzymes and blood proteins. Research has shown that these metabolites form adducts with CYP3A4 itself and with plasma proteins, which may partly explain the liver toxicity occasionally seen with the drug and could contribute to drug interactions.²⁸ Liver function tests are part of routine monitoring during sunitinib treatment for this reason.

Investigational Uses and Ongoing Research

Sunitinib has been tested against cancer types beyond its three approved indications, with mixed results. In triple-negative breast cancer, preclinical work showed the drug could suppress tumor growth, migration, and blood vessel formation. However, the same research flagged a concerning finding: sunitinib appeared to increase the number of breast cancer stem cells, a subpopulation thought to drive recurrence and resistance.²⁹ This kind of double-edged finding, where a drug shrinks the tumor bulk but potentially enriches the most dangerous cell population, has been a recurring theme in sunitinib research outside its approved settings and helps explain why the drug’s approvals remain limited to specific tumor types despite its broad kinase-inhibiting profile.

Research into combining sunitinib with other agents continues as well, particularly in settings where resistance develops. Strategies under investigation include pairing sunitinib with drugs that disrupt the lysosomal trapping mechanism, combining it with agents targeting the alternative pathways tumors use to escape, and sequencing it after immunotherapy rather than before. The drug may be nearly two decades old, but its story is still being written.