How Does Alectinib Work? — The ALK Target and the Pathway It Blocks

No. Alectinib is a targeted therapy — a different class of treatment from chemotherapy. Chemotherapy works by attacking all rapidly dividing cells, including healthy hair follicles, gut lining, and blood cells, which is why it causes hair loss, nausea, and low blood counts. Alectinib blocks one specific protein. Its side effects are different and, for most people, different in character from chemotherapy, though they are real and worth discussing with your oncologist.

Yes. Alectinib only works if your cancer has an ALK gene rearrangement, confirmed by biomarker testing on your tumour tissue. Without that rearrangement, there is nothing for the drug to target and it will not help. If you have been prescribed alectinib, your oncologist will have confirmed this rearrangement from your biopsy results. If you are unsure whether the testing was done or what it showed, ask for the results in writing.

The aim is to control the cancer for as long as possible — to stop it growing and spreading, and in many cases to cause it to shrink. Whether that translates to a very long remission depends on factors individual to your cancer. Oncologists treating metastatic cancer with targeted therapy use words like 'control' and 'response' rather than 'cure', because those words are more accurate. What is worth knowing is that responses to alectinib can be durable, lasting years in a proportion of patients according to ASCO and ESMO data.

For many people, eventually yes. Cancer cells can develop further mutations that let them grow despite alectinib — a process called acquired resistance. When imaging shows the cancer progressing after a period of control, your oncologist will assess where it is growing and may recommend a biopsy to identify which resistance mechanism has developed. There are further ALK inhibitors, including lorlatinib, and the approach at that point depends on how and where the cancer has progressed.

The main tool is imaging — usually a CT scan of the chest and abdomen, and an MRI of the brain if there was involvement there. These are scheduled at intervals your oncologist will set from the start of treatment. A scan showing the tumour shrinking or stable is a positive response. You may not notice a change in how you feel in the first few weeks, so do not use symptoms alone as a guide to whether the treatment is working. If you feel clearly worse at any point, contact your team rather than waiting.

ALK is largely inactive in healthy adult tissue, which means alectinib's main effect is on cells where ALK is still driving growth — the cancer cells. That said, alectinib does have side effects, including muscle aches, increased sensitivity to sunlight, fluid retention in the hands and feet, and occasional changes in liver enzymes picked up on blood tests. Your team will monitor through regular blood tests and will advise on managing any reactions. These differ from chemotherapy side effects and are generally manageable for most people.