Crizotinib for Cancer: Uses, Side Effects, and Warnings

Crizotinib (brand name Xalkori) is a targeted cancer drug that works by blocking specific abnormal proteins driving tumor growth, primarily in certain types of lung cancer. It was the first drug approved by the FDA, in 2011, for non-small-cell lung cancer (NSCLC) that carries a rearrangement in the ALK gene, and it has since gained approvals for tumors with ROS1 gene rearrangements and for select rare cancers in children and young adults. While crizotinib represented a breakthrough when it arrived, the landscape around it has shifted considerably: newer drugs in the same family now outperform it in head-to-head trials, and its side-effect profile, which includes vision changes, liver stress, and rare but serious lung inflammation, remains an important part of any treatment conversation.

What Crizotinib Treats

Crizotinib’s primary use is in advanced NSCLC that tests positive for certain gene alterations. The most established indication is ALK-positive NSCLC, a subtype found in a small fraction of all lung cancers. ALK rearrangements cause cells to produce a fusion protein that acts as a constant growth signal. Crizotinib binds to that protein and shuts down the signal, slowing or shrinking the tumor.¹

The drug also targets ROS1-rearranged NSCLC, a rarer molecular subtype. In a key study, patients with advanced ROS1-positive disease treated with crizotinib had an objective response rate of about 72%, and their median progression-free survival reached roughly 19 months.² Updated follow-up from the same study found a median overall survival exceeding four years, with half of patients still alive at the 48-month mark.³

Beyond lung cancer, crizotinib carries a pediatric approval in the United States for children aged one year and older and young adults with relapsed or hard-to-treat ALK-positive anaplastic large cell lymphoma (ALCL) and for unresectable or recurrent ALK-positive inflammatory myofibroblastic tumor (IMT).⁴ In a Children’s Oncology Group study, response rates were around 83–90% in ALCL and 86% in IMT, with many patients achieving complete responses.⁵

How Well It Works in ALK-Positive Lung Cancer

Two landmark trials established crizotinib’s efficacy in ALK-positive NSCLC. In patients who had already received prior chemotherapy, crizotinib roughly doubled progression-free survival compared with standard chemotherapy (about 7.7 months versus 3 months) and achieved a response rate of 65% versus 20% for chemotherapy.⁶ When used as an initial treatment in newly diagnosed patients, the advantage persisted: median progression-free survival was about 11 months with crizotinib compared with 7 months for chemotherapy, and the response rate climbed to 74%.⁷

An earlier phase I/II expansion study in a broader group of ALK-positive patients reported a response rate of about 61%, with responses appearing quickly (median time to first response around eight weeks) and lasting close to a year on average.⁸ These numbers were remarkable at the time, because ALK-positive patients had no targeted option before crizotinib.

Quality-of-life data reinforced the clinical numbers. In a head-to-head comparison with chemotherapy, patients on crizotinib reported significantly better physical functioning, less fatigue, less pain, and less shortness of breath. The trade-off was more diarrhea and constipation on crizotinib, though overall quality of life still favored the targeted drug.⁹

MET-Driven Lung Cancers

Crizotinib also hits the MET protein, which has opened a door for patients whose tumors carry MET exon 14 skipping mutations, a distinct molecular alteration found in a small percentage of lung adenocarcinomas. In a retrospective analysis, patients with MET exon 14 skip mutations treated with crizotinib had a median progression-free survival of about 12 months and a median overall survival approaching two years.¹⁰ Early case series first demonstrated that tumors harboring these mutations could indeed respond to MET-targeted therapy.¹¹ Patients with MET gene amplification alone, however, fared much worse on crizotinib, with progression-free survival of only about 2.6 months, suggesting the specific type of MET alteration matters a great deal.¹⁰ Newer MET-specific inhibitors like capmatinib and tepotinib have since gained dedicated approvals for MET exon 14 skip mutations, but crizotinib remains part of the conversation, especially when access to newer agents is limited.

Common Side Effects

Most people taking crizotinib experience side effects, but the majority are mild to moderate. The most frequent complaints fall into a few predictable categories:

• Vision changes: Flashing lights, light trails, blurred vision, or sensitivity to brightness are reported by a majority of patients. Research into the mechanism suggests that crizotinib directly alters how retinal cells fire, affecting roughly 40% of examined cells in laboratory models, which likely explains the visual disturbances that many patients notice almost immediately after starting treatment.¹²
• Gastrointestinal issues: Nausea, vomiting, diarrhea, and constipation are common. These tend to be manageable with standard anti-nausea medications and dietary adjustments.
• Fatigue and edema: Tiredness and swelling in the legs or around the eyes occur in a significant number of patients.
• Taste changes: Food may taste metallic or simply “off.” This is bothersome but not dangerous.

These side effects, while inconvenient, rarely force patients to stop treatment. Proactive monitoring and early intervention can keep most of them under control.¹³

Liver Toxicity

Liver enzyme elevations are one of the more closely watched side effects with crizotinib. A large meta-analysis comparing crizotinib to newer-generation ALK inhibitors found that crizotinib carried a higher risk of all-grade liver enzyme (ALT) elevation than several of its successors. Drugs like alectinib and brigatinib were each associated with significantly lower rates of liver enzyme increases. For severe elevations (grade 3 or higher), alectinib and brigatinib again showed statistically meaningful reductions in risk compared with crizotinib.¹⁴ This means your oncology team will order regular blood tests to track liver function while you are on crizotinib, typically every couple of weeks at first and then at longer intervals if levels stay stable.

For patients who already have liver impairment before starting treatment, dose adjustments are necessary. No change is needed for mild impairment, but moderate impairment calls for a reduced dose (200 mg twice daily instead of the standard 250 mg twice daily), and severe impairment requires a further reduction, with the daily dose capped at 250 mg total per day rather than the usual 500 mg.¹⁵

Serious Warnings

Interstitial Lung Disease

The most dangerous potential complication of crizotinib is interstitial lung disease (ILD), a type of severe lung inflammation that can be fatal. An independent review spanning four large crizotinib trials found new-onset ILD in about 1.2% of patients overall. The mortality rate among those who developed ILD was 50%, though outcomes improved substantially when crizotinib was stopped as soon as symptoms appeared: nine out of fourteen patients survived with early discontinuation, compared with just one out of six when the drug was continued or stopped later.¹⁶

ILD risk is not evenly distributed. In a large Japanese post-marketing study, the incidence was considerably higher at about 5.8%, with most cases surfacing within the first eight weeks. Risk factors identified included age 55 and older, poor physical performance status, smoking history, pre-existing lung disease, and the presence of fluid around the lungs.¹⁷ The higher rate in this Japanese cohort compared with the roughly 1% seen in predominantly Western trial populations is worth knowing about if you or a family member is starting crizotinib, because it speaks to genuine variability in susceptibility. Any new or worsening cough, shortness of breath, or fever while on crizotinib should be reported to your care team immediately.

Heart-Related Effects

Crizotinib can slow the heart rate (bradycardia) and prolong the QT interval on an electrocardiogram, which in rare cases raises the risk of abnormal heart rhythms.¹⁸ Heart failure is a rarer complication but has been documented. One published case involved a patient who initially developed bradycardia and QT prolongation, then progressed to heart failure even after the crizotinib dose was reduced.¹⁹ Routine EKG monitoring and heart-rate checks are standard practice while on this drug, and patients on medications that also slow the heart or lengthen the QT interval need especially careful oversight.

Drug Interactions

Crizotinib is processed in the liver by the CYP3A enzyme system, and it also inhibits and weakly induces that same system.²⁰ In practical terms, this means drugs that strongly boost or block CYP3A can change how much crizotinib ends up in your bloodstream. Strong CYP3A inhibitors, such as certain antifungal medications and some antibiotics, can raise crizotinib levels and increase the chance of side effects. Conversely, strong CYP3A inducers like rifampin and certain anti-seizure drugs can lower crizotinib levels enough to reduce its effectiveness. Your oncologist and pharmacist will review your full medication list, including over-the-counter drugs and supplements like St. John’s wort, before starting treatment. Grapefruit juice is another common CYP3A inhibitor that patients are typically told to avoid.

Why Tumors Eventually Stop Responding

Despite impressive initial responses, most patients on crizotinib develop resistance within one to two years. Research into resistant tumors has identified several mechanisms. In roughly one-quarter of cases, the ALK gene itself changes: new mutations pop up in the enzyme’s active site or the ALK fusion gene gets amplified, producing more protein than crizotinib can block.²¹ In other cases, the tumor finds entirely new growth pathways to exploit, bypassing ALK altogether.²²

This diversity of escape routes is why oncologists typically re-biopsy tumors at progression and sometimes use blood-based genetic testing: knowing which resistance mechanism is at play can guide the next line of therapy. Many patients who develop resistance to crizotinib still respond to newer ALK inhibitors, making the sequence of treatments just as important as the choice of first drug.

The Brain Metastasis Problem

One of crizotinib’s most meaningful limitations is its poor ability to penetrate the blood-brain barrier. The brain is a common site of spread for ALK-positive and ROS1-positive lung cancers, and crizotinib often struggles to control disease there even while keeping the rest of the body in check. In patients with ROS1-rearranged NSCLC, brain progression on crizotinib was a frequent event, and researchers have concluded that poor central-nervous-system penetration remains a major source of disease burden for both ROS1-positive and ALK-positive patients.²³

Real-world data from the METROS study reinforced this point. Among ROS1-positive patients, those who had brain metastases at the start of crizotinib treatment had notably shorter progression-free survival (about 7 months) compared with those whose cancer had not yet spread to the brain (about 17 months). Overall survival showed a similar pattern: roughly 16 months with brain involvement versus about 43 months without it.²⁴ This gap is a major reason why newer drugs with better brain penetration have largely replaced crizotinib as a first choice for ALK-positive disease.

How Newer ALK Inhibitors Compare

The oncology field has moved fast since crizotinib’s approval. Second-generation drugs like alectinib and brigatinib, and the third-generation drug lorlatinib, all target the same ALK fusion protein but were designed to overcome crizotinib’s weaknesses, especially poor brain penetration and vulnerability to common resistance mutations.

The CROWN trial compared lorlatinib head-to-head with crizotinib as a first-line treatment. After three years of follow-up, 64% of patients on lorlatinib were still alive without disease progression, compared with 19% on crizotinib. The hazard ratio for progression or death strongly favored lorlatinib. The difference in brain control was even more striking: in patients without brain metastases at the start, just 1% of the lorlatinib group developed brain progression, compared with 23% of those on crizotinib.²⁵ At the initial 12-month mark, 78% of lorlatinib patients remained progression-free versus 39% on crizotinib, and among patients with measurable brain metastases, lorlatinib produced an intracranial response in 82% versus 23% for crizotinib.²⁶

Cross-trial comparisons between alectinib and lorlatinib suggest lorlatinib may have a further edge, with a higher rate of complete brain responses and a lower cumulative risk of brain progression.²⁷ These results have shifted guidelines in many countries toward recommending a second- or third-generation ALK inhibitor rather than crizotinib as the initial treatment for ALK-positive NSCLC. Crizotinib still has a role when newer agents are unavailable or not tolerated, and it remains a standard first-line option for ROS1-positive disease, where the evidence base for alternatives is less mature.

Testing Before Treatment

You cannot benefit from crizotinib unless your tumor carries one of the gene alterations the drug targets. Testing for ALK rearrangements was originally done with a specific fluorescence in situ hybridization (FISH) kit that the FDA approved alongside crizotinib as a companion diagnostic.²⁸ Since then, immunohistochemistry (a simpler staining method) and next-generation sequencing (which reads large stretches of tumor DNA at once) have become widely used alternatives. All three methods can reliably identify ALK fusions, though sequencing has the advantage of simultaneously detecting ROS1 and MET alterations as well.²⁹

If you’ve been diagnosed with advanced NSCLC and molecular testing has not been discussed, ask about it. Comprehensive genomic profiling can uncover not only ALK and ROS1 rearrangements but also MET exon 14 mutations and other actionable alterations. This testing is now considered standard of care for anyone with advanced non-squamous NSCLC and is increasingly used in other lung cancer subtypes as well.

The Pediatric Formulation

When crizotinib expanded into pediatric use for ALCL and IMT, a significant practical barrier emerged: young children often cannot swallow capsules. Pfizer developed a multiparticulate formulation consisting of small coated pellets packaged inside capsules that can be opened. The pellets are sprinkled directly into the child’s mouth or mixed with soft food, and the correct dose is achieved by combining different capsule strengths.⁴ This might seem like a minor detail, but for families managing cancer treatment in a toddler or young child, the ability to give an oral targeted therapy without forcing a capsule can meaningfully affect compliance and daily life.

One caveat from the pediatric ALCL data is that while initial responses to crizotinib are strong, a large proportion of patients relapse after stopping the drug, raising questions about whether longer or indefinite courses of treatment might be needed for a durable cure in this setting.³⁰ This remains an active area of clinical research, and families should discuss the expected treatment duration and monitoring plan with their pediatric oncologist.