Cancer Found Accidentally (Incidentalomas)

This page is for people told a scan found an unexpected mass. It explains how common these findings are, how doctors usually check them, and the trade-offs of more testing.

An incidentaloma is a mass found by accident, on a scan done for an unrelated reason. The scan answers the question it was asked. Then it reports something else as well.

Incidental findings can be common in some settings. The USPSTF reviewed lung cancer screening trials. It reported that studies found a wide range of screening-related incidental findings deemed significant or needing further evaluation, from 4.4 percent to 40.7 percent of participants.

In the National Lung Screening Trial, cancers of the kidney, thyroid or liver were ultimately diagnosed in 0.39 percent of participants in the CT group during screening. These figures come from a lung cancer screening trial, so they may not match your situation. Only your care team can say what your own finding most likely is.

The American College of Radiology (ACR) publishes white papers from its Incidental Findings Committee. The ACR says that when guidance on effective management is not available, there is potential for over-testing and over-treatment of incidental findings associated with very low risk. The next step depends on the finding. Ask your care team what they recommend and why.

Investigation is not free.

The USPSTF review reported NLST false-positive rates of 26.3 percent at baseline, 27.2 percent in year 1 and 15.9 percent in year 2. Working up those false positives led to invasive procedures in 1.7 percent of screened participants, with complications in 0.1 percent. In the wider review, complications from needle biopsy for false-positive results ran 0.03 to 0.07 percent of all those screened, and surgical procedures for false positives followed in 0.5 to 1.3 percent.

NCI's screening guidance names the same problems. A false-positive test result "can cause anxiety and is usually followed by more tests and procedures, which also have risks". And there is overdiagnosis, which means finding cancers that "would have gone away on their own or never caused any symptoms". NCI says there is no way to know if treating the cancer would help the person live longer than if no treatment were given.

A useful question to ask your care team is what they think the finding most likely is, what they recommend next, and why. Asking turns an open-ended worry into a defined plan. If you notice new symptoms, or you are told something urgent, call your care team right away.

• USPSTF — Lung Cancer Screening recommendation (harms, incidental findings)
• NCI PDQ — Cancer Screening Overview (harms of screening)
• NCI — National Lung Screening Trial