Cancer Genomics
Your Cancer Is Not My Cancer: What Tumour DNA Is Changing About Treatment
Two people can have the same cancer diagnosis, receive the same treatment, and have completely opposite outcomes — and scientists now know exactly why.
The Idea
For most of modern medicine's history, cancer was classified by where it appeared in the body: breast cancer, lung cancer, colon cancer. Treatment followed the same logic — if it's in the lung, here's the protocol. This turned out to be a profound oversimplification. What cancer actually is, at its core, is a disease of corrupted DNA. And the mutations driving one person's lung tumour can be entirely different from the mutations driving another's. Two patients with 'the same' diagnosis may, genetically speaking, have almost nothing in common. Cancer genomics is the field that takes this seriously. By sequencing the DNA of a tumour — reading its full genetic code — oncologists can now identify which specific mutations are fuelling its growth. Some of those mutations have known weak points: proteins they produce that can be targeted by drugs designed to fit them like a key in a lock. These are called targeted therapies, and they work dramatically better than broad-spectrum chemotherapy for patients whose tumours carry the right mutation. What makes this genuinely remarkable is the reversal it represents. Instead of asking 'where is the cancer?' medicine is increasingly asking 'what is the cancer doing at the molecular level, and what does that tell us about how to stop it?' A melanoma patient and a lung cancer patient might now receive the same drug — because their tumours share the same driving mutation, even though the cancers look nothing alike from the outside. Location becomes secondary. Genomic identity becomes primary.
In the World
In 2011, a woman named Sharon Belvin was facing a terminal prognosis. She had metastatic melanoma — a cancer that, at the time, was nearly always fatal once it had spread. Standard chemotherapy had failed her. Then her oncologist, at Memorial Sloan Kettering Cancer Center in New York, tested her tumour's DNA and found something specific: a mutation in a gene called BRAF. About half of all melanomas carry this mutation, and it essentially acts as a stuck accelerator, telling cancer cells to keep dividing without stopping. A drug called vemurafenib had been designed precisely to block the protein produced by mutated BRAF. Belvin was enrolled in a trial. Within weeks, her tumours began to shrink. She became one of the early, striking examples of what genomically targeted therapy could do — not just slowing cancer, but sending it into retreat. The BRAF story has since expanded. The same mutation appears in some thyroid cancers, colon cancers, and brain tumours. When it does, the same class of drugs often applies — a complete inversion of the old tissue-based logic. Today, the FDA has approved treatments that are indicated not by the location of the cancer but purely by its genetic profile, regardless of organ of origin. These are called tumour-agnostic approvals, and they represent one of the sharpest conceptual breaks in oncology's history. The cancer's address no longer determines its treatment. Its molecular fingerprint does.
Why It Matters
You may not be dealing with cancer right now, and hopefully you won't be for a long time. But this shift in how medicine thinks about disease carries a broader implication worth sitting with: categories are often proxies for something more fundamental that we haven't yet learned to measure. For decades, 'lung cancer' felt like a precise, actionable category. It wasn't — it was a rough approximation waiting for better tools. The same is probably true of many things we currently treat as fixed categories in medicine, psychology, and beyond. What we call depression, for instance, is almost certainly multiple distinct conditions that share surface symptoms but have different underlying mechanisms — and the treatments that work brilliantly for one subtype do almost nothing for another. On a practical level, if you or someone you care about ever faces a cancer diagnosis, knowing that tumour genomic testing exists — and asking for it — could be one of the most important questions in the room. Not all oncologists offer it routinely for all cancer types yet. Understanding that the biology of a specific tumour matters as much as its location is knowledge that can help you ask better questions and advocate more effectively.
A Question to Ponder
What other categories in your life — personality types, diagnoses, labels for people or problems — might be rough approximations concealing important differences underneath?
Get a new one of these every morning.
Start learning with Thinkable