During or after cancer treatment, a chest CT scan sometimes reveals one or more small spots in the lungs, called pulmonary nodules. When these first appear, a single image often cannot tell whether they are metastases (spread of cancer) or something harmless, such as an old scar or a trace of past inflammation. For this reason, doctors frequently choose to repeat the scan at set intervals and watch how the nodules change over time — an approach often called active surveillance or watchful waiting.
Why does change in size matter so much? Metastatic lesions tend to grow gradually over time, while a spot that stays the same for a long period, or shrinks, is less likely to be cancer. This is why your care team pays close attention to the growth rate of a nodule. Still, this reasoning is based on probability rather than certainty. Some nodules grow so slowly that the change only becomes visible after several scans.
In real life, the pattern can look irregular — stable for a while, slightly larger at one point, then stable again. Part of this is because measurements can vary by a few millimeters depending on who measures, the scan settings, and how deeply the person breathed in. Part of it reflects the nature of the lesion itself. This is why the overall trend across several scans matters more than any single result.
So why not simply do a biopsy to be sure? When a nodule is very small, deep within the lung, or close to large blood vessels, passing a needle to collect tissue carries a higher risk of complications such as a collapsed lung (pneumothorax) or bleeding. A small target is also easy to miss, which can produce an inconclusive result. Weighing these risks against the information gained, doctors sometimes decide that careful observation is the safer and more useful choice.
Among people in similar situations, some are eventually diagnosed with metastasis and begin treatment, while others continue observation because nothing changes. There is no single fixed path; the direction depends on the original cancer type, the shape and number of nodules, and overall health. At your appointment, it can help to ask specific questions: how the doctor is currently interpreting the lesion, when the next scan should be, and what the plan would be if it grows.
Above all, remember that the long wait itself can be a heavy burden. Living with uncertainty for months or years is exhausting, and sharing that feeling with your care team or someone close to you is also part of the healing process.
This article is for general information only and does not replace individual medical care. Please discuss your own test results and treatment plan with your healthcare team.