Cancer is not just one disease. Even two people with the “same” cancer type—such as breast cancer or lung cancer—can have very different cancers at the genetic level. That is why modern cancer care is moving beyond looking only at where the cancer started, and toward understanding what is happening inside the tumor’s DNA. This is called tumor genetic testing or tumor profiling, and it is helping doctors choose treatments that are more precise and more effective.
To understand tumor genetics, it helps to first know the difference between inherited mutations and tumor mutations. Inherited mutations (also called germline mutations) are changes in DNA that you are born with. They are present in almost every cell of the body and can be passed on in families. These inherited changes can increase a person’s risk of developing certain cancers, but they are not the whole story. Tumor mutations (also called somatic mutations) develop later in life in a specific group of cells. They are not present at birth and are usually not passed on to children. Most cancers happen because cells gradually collect these tumor mutations over time, until they begin growing uncontrollably.
A tumor genome test looks specifically at the DNA changes inside the cancer cells. It can reveal “driver mutations,” which are the key genetic changes that push the cancer to grow and survive. Identifying these drivers is important because some cancers rely heavily on one main driver pathway, and blocking that pathway can slow down or stop the cancer. Tumor testing can also reveal resistance markers—genetic changes that explain why a cancer may not respond to a certain treatment, or why it stopped responding after initially improving. This information can help doctors avoid ineffective therapies and consider better options sooner.
One of the biggest benefits of tumor genetic testing is that it can guide targeted therapy. Targeted therapies are medicines designed to attack cancer cells based on specific genetic changes, often with fewer side effects than traditional chemotherapy. For example, in breast cancer, some tumors have changes in genes such as HER2 or PIK3CA, and treatments may be chosen specifically to block those signals. In lung cancer, certain tumors carry mutations like EGFR or rearrangements like ALK, and patients with these changes may respond very well to targeted tablets instead of standard chemotherapy. These treatments can sometimes lead to better disease control and improved quality of life.
Tumor genetics can also influence decisions about immunotherapy, a type of treatment that helps the immune system recognize and fight cancer. Some genetic patterns in tumors may suggest that immunotherapy is more likely to work, while others may suggest a lower chance of benefit. This helps doctors personalize treatment plans rather than using the same approach for everyone.
Most importantly, tumor profiling can change real treatment outcomes. It can help doctors choose therapies that match the biology of the cancer, reduce time spent on trial-and-error treatments, and guide next steps if the cancer changes over time. In some cases, repeating tumor testing later can help identify new mutations that explain why the cancer has become resistant and what new treatments may work.
Cancer is deeply personal, and every patient wants the best chance at the right treatment. Tumor genetic testing helps make cancer care more precise by revealing what is driving an individual tumor. By understanding the cancer’s DNA, doctors can make more informed choices, improve treatment strategies, and offer care that is increasingly tailored to the person—not just the cancer type.
