Studies comparing narrow, hotspot-only panels with broader testing have found that broadening the panel turns up an actionable result for many patients who had none on the narrow panel, and identifies matched therapies more often. Broad testing also keeps working over time. In one analysis of more than 47,000 tumors, the share of patients whose existing results pointed to a standard-of-care targeted treatment rose from about 9 percent in 2017 to about 32 percent in 2022, with no new testing, simply because more treatments had been approved in the meantime. Medical groups increasingly recommend broader testing, especially for advanced-stage cancer.

This gap matters most for advanced or previously treated cancers, where resistance mutations and rarer alterations with targeted treatments available are common but often sit outside a standard hotspot panel.

How broadly a test reads your tumor can also change how certain markers are scored. Independent studies have found that smaller gene panels and whole-exome sequencing often disagree when measuring tumor mutational burden, a marker used to decide whether immunotherapy is likely to help. Panels that read less than about one million bases of DNA carry enough error to put some patients on the wrong side of the cutoff. In one analysis of patients receiving the immunotherapy pembrolizumab, the patients that whole-exome scoring called high, and smaller panels called low, lived about five months longer than the group scored the other way around. If this marker matters in your case, ask your oncologist how it was measured.

Gene fusions occur across many cancer types, not just one or two, and finding one may open the door to a precision therapy designed to target it. Because DNA-only testing can miss fusions that RNA testing detects, analyzing both can provide the most complete picture of your cancer.

Fusions can occur in any cancer type. RNA testing is especially important in cancers such as lung, thyroid, bile duct, sarcoma, and gliomas, especially in children, where they are more common.

This isn't rare. In one study of patients with advanced cancer, about half of the mutations found in blood came from these aging blood cells rather than from the tumor. Without a way to tell the two apart, a patient can be recommended a targeted drug for a mutation that is not actually in their tumor.

The fix is straightforward: ask your oncologist if the blood test they plan to use can tell the difference and remove CHIP from the decision-making process.

The two that matter most in solid tumors are DPYD and UGT1A1. DPYD controls how your body clears fluorouracil and capecitabine, the backbone of treatment for colorectal, stomach, pancreatic and some breast cancers. UGT1A1 controls how your body clears irinotecan, used in colorectal and pancreatic regimens. The FDA labeling for fluorouracil and capecitabine now tells doctors to consider DPYD testing before treatment begins, and the irinotecan labeling describes a lower starting dose for people who carry reduced-function UGT1A1.

In blood cancers the genes are different. TPMT and NUDT15 affect thiopurines such as mercaptopurine and azathioprine, used in the long maintenance phase of acute lymphoblastic leukemia, where reduced function can cause life-threatening drops in blood counts. G6PD affects rasburicase, given for tumor lysis syndrome, which carries a boxed warning for severe red blood cell destruction. None of the blood cancer panels listed on this site report any of these, so they have to be requested separately.

Timing is the whole point. These are inherited differences you have had since birth, not changes in the tumor, so the result does not expire and one test lasts a lifetime. It is only useful if it comes back before the first dose. Results usually take about a week, and the guidelines describe specific dose reductions rather than stopping treatment, so for most people this is an adjustment, not a closed door.

Because the result is inherited, a reduced-function result can also matter to parents, siblings and children who may one day need the same drugs. If yours comes back abnormal, ask whether it is worth mentioning to close relatives.

In published research, Caris' GPSai returned a likely tissue of origin for the large majority of the cancers of unknown primary it was run on. Across all tumors profiled, not only those of unknown origin, it also prompted a change to the original diagnosis in a small share of cases, and in most of those the change affected which targeted treatments the patient qualified for.