ALK-Positive Lung Cancer: Meaning

ALK stands for anaplastic lymphoma kinase. It is a gene that makes a signaling protein. In healthy adult lung tissue it is mostly quiet.

In ALK-positive lung cancer, a piece of chromosome has broken and rejoined the wrong way. The ALK gene ends up fused to a neighbor. The National Cancer Institute (NCI) describes the common version this way: "ALK::EML4 fusion genes form translocation products that occur in 3% to 7% of unselected NSCLC cases." NCI adds that "sensitizing fusions of ALK with other genes have also been reported."

The word fusion is the key. This is not a typo in one letter of DNA. It is two genes spliced together, and the hybrid protein is stuck in the on position. That is why a drug that blocks it can work so dramatically. You are switching off a jammed switch, not correcting a slow leak.

Roughly 3 to 7 in every 100 non-small cell lung cancers carry it. That is small enough to miss if nobody tests, and large enough that everyone with non-small cell lung cancer should be tested.

Reports use several phrasings: ALK rearranged, ALK fusion detected, ALK positive, or no ALK alteration detected. Different methods sit behind those words.

One method stains the tumor for ALK protein. The Food and Drug Administration (FDA) named a specific version of that stain, the VENTANA ALK (D5F3) CDx assay, as a companion diagnostic when it approved alectinib after surgery. A companion diagnostic is a test formally tied to a drug approval. FDA allows a locally performed FDA-approved ALK test as well.

Other methods look at the DNA or RNA directly. Sequencing panels can name the exact partner gene and the exact breakpoint. That extra detail matters later, if the cancer stops responding.

Ask three things about your own result: which method was used, whether the partner gene was identified, and whether the sample was tissue or blood. NCI notes that a liquid biopsy is a blood draw rather than a tissue sample. Blood tests are easier but can miss what tissue would show.

Every one of these is a pill. NCI lists the approved uses.

• Crizotinib (Xalkori). Approved for "non-small cell lung cancer that is ALK positive or ROS1 positive and has spread to other parts of the body."
• Ceritinib (Zykadia). Approved for "non-small cell lung cancer that is ALK positive and has metastasized (spread to other parts of the body). It is used in adults."
• Alectinib (Alecensa). Approved both "to prevent NSCLC from coming back after it was removed by surgery" and "in patients whose NSCLC has spread to other parts of the body."
• Brigatinib (Alunbrig). Approved for metastatic ALK-positive NSCLC in adults.
• Lorlatinib (Lorbrena). Approved for "non-small cell lung cancer that is ALK positive and has spread to other parts of the body."
• Ensartinib (Ensacove). FDA approved it on December 18, 2024 for "adult patients with anaplastic lymphoma kinase (ALK)-positive locally advanced or metastatic non-small cell lung cancer (NSCLC) who have not previously received an ALK-inhibitor."

Notice how the labels differ. Only one of them currently covers use after surgery. Only one covers a second gene, ROS1. Those differences drive real decisions.

For years, targeted drugs were for advanced disease only. That changed for ALK.

On April 18, 2024, FDA approved alectinib for "adjuvant treatment following tumor resection in patients with ALK-positive NSCLC." Eligibility runs from resectable Stage IB, meaning tumors 4 cm or larger, through Stage IIIA, using the AJCC 7th edition staging system.

The evidence came from the ALINA trial, which randomly assigned 257 patients after surgery to either alectinib or platinum-based chemotherapy. For disease-free survival, the hazard ratio was 0.24. Median disease-free survival was not reached in the alectinib group, versus 41.3 months with chemotherapy in the overall population.

A hazard ratio of 0.24 means the rate of recurrence or death was about a quarter of the comparison group's rate during the study. The dose FDA lists is "600 mg orally twice daily with food for 2 years or until disease recurrence or unacceptable toxicity." Read that as the label's benchmark. Your oncologist may start you lower or trim it later for liver results or muscle aches, and the prescription you are handed is the one to follow.

FDA lists these side effects in at least 20% of patients: liver toxicity, constipation, muscle pain, COVID-19, fatigue, rash, and cough. Liver toxicity is why blood tests are scheduled, not optional.

The practical lesson: if your tumor was removed and nobody ran ALK testing, ask why. This is a stage where testing changes what happens next.

The ensartinib approval rested on eXALT3, an open-label randomized trial in 290 patients who had never had ALK treatment. It compared ensartinib against crizotinib.

Median progression-free survival was 25.8 months with ensartinib versus 12.7 months with crizotinib, a hazard ratio of 0.56. Overall survival showed no statistically significant difference between the groups. The labelled amount is 225 mg by mouth once daily, carrying on until the cancer progresses or the side effects become unmanageable — again, subject to whatever your own team prescribes. Side effects reported in at least 20% of patients included rash, musculoskeletal pain, constipation, cough, itching, nausea, swelling, fever, and fatigue.

Two things are worth taking from that. Newer ALK drugs have generally beaten crizotinib on how long the cancer stays controlled. And a longer control period does not automatically mean a proven survival difference in a single trial.

Crizotinib is worth knowing about even outside lung cancer, because ALK fusions appear in other tumors. NCI lists it for "anaplastic large cell lymphoma that is ALK positive and systemic" in children aged 1 and older and young adults with relapsed or refractory disease, and for "inflammatory myofibroblastic tumor that is ALK positive" in adults and children aged 1 and older with relapsed, refractory, or unresectable disease.

If you are reading this for a child or for a rare soft tissue tumor, that is the reason ALK came up.

NCI notes that "the biomarkers in your cancer can change over time," and that a provider "may want to test your cancer again, for example, if it comes back after treatment."

That is the whole logic of retesting in ALK-positive disease. Cancers that stop responding often have acquired a new change inside the ALK gene itself. Which change it is can point toward a different ALK drug. So a biopsy or blood test at progression is not a formality.

Which test found my ALK result, and which partner gene was identified? Was it run on tissue, on blood, or both? If my tumor was removed, am I eligible for alectinib after surgery under the stage rules? Which drug are you starting me on, and what is the evidence against crizotinib for that choice? Do I have brain imaging, and does that affect which drug you pick? What blood tests will monitor my liver? At progression, will you rebiopsy or use a blood test to look for a resistance change? Is there an ALK-specific clinical trial for me?

• Call 911 or go to an emergency department if you cough up blood, have sudden chest pain, or are breathless while sitting still.
• Call 911 or go to an emergency department if a first seizure happens, or weakness on one side, new trouble speaking, or a sudden loss of balance comes on. ALK-positive lung cancer reaches the brain often enough that brain imaging is part of the workup, and signs like these need imaging within the hour, not a clinic appointment.
• Call your care team the same day if shortness of breath or a cough is new or getting worse. The ALK drugs can inflame the lungs, and that is not something to wait out.
• Call your care team within a day or two if the whites of your eyes turn yellow, pain settles under your right ribs, or your appetite falls away. These point to liver injury, which is what the routine blood tests are looking for.
• Call your care team within a day or two if you get sudden muscle pain, tenderness or weakness, or if you feel dizzy or faint.

Start with Biomarker Testing, Understanding Your Pathology Report, and Targeted Therapy vs Chemotherapy.

• https://www.cancer.gov/types/lung/hp/non-small-cell-lung-treatment-pdq
• https://www.cancer.gov/about-cancer/treatment/types/biomarker-testing-cancer-treatment
• https://www.cancer.gov/about-cancer/treatment/drugs/alectinib
• https://www.cancer.gov/about-cancer/treatment/drugs/crizotinib
• https://www.cancer.gov/about-cancer/treatment/drugs/ceritinib
• https://www.cancer.gov/about-cancer/treatment/drugs/brigatinib
• https://www.cancer.gov/about-cancer/treatment/drugs/lorlatinib
• https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-alectinib-adjuvant-treatment-alk-positive-non-small-cell-lung-cancer
• https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-ensartinib-alk-positive-locally-advanced-or-metastatic-non-small-cell-lung-cancer
• https://medlineplus.gov/druginfo/meds/a616007.html