Can A Ct Scan Miss Cancer
Most people know that imaging tests like X-rays and MRIs are great for examining internal organs and bones. They’re also useful when looking for broken bones or foreign objects lodged in the body. But imaging tests aren’t always so reliable when it comes to detecting cancer. In fact, they might not even be able to do that very well sometimes. That’s because some types of cancers don’t show up on an image as easily as others. And certain parts of the body have more trouble with imaging tests than others. So how accurate is this technology?
How often does a test misdiagnose someone as having cancer? It depends on which type of test you’re using. For example, mammograms tend to detect breast cancer better than any other type of test, including MRI, ultrasound and CAT scans. The same goes for bone density testing; those who need them most are far more likely to receive a positive result from an x-ray than anyone else. Other ways in which different tests may perform differently include:
A patient with lung cancer may appear normal on chest x-ray but could actually have metastatic disease (cancer cells spread throughout the body)
An abdominal tumor growing in a woman’s ovaries may not be visible on her routine pelvic exam but will show up on a transvaginal sonogram
A brain tumor may look unremarkable on a head CT but may become apparent during a follow-up study months later.
The problem isn’t necessarily one of sensitivity – there’s enough radiation involved in regular diagnostic procedures to cause problems. More often, the issue is specificity, meaning that the test doesn’t pick up every instance of cancer. This occurs partly because many types of cancers exhibit similar symptoms, such as indigestion and weight loss. Also, most forms of cancer are slow-growing. When a test misses something early on, it’s more likely to overlook it completely rather than mistake it for something benign.
But what about CT scans? Are they really as good as we think at finding all kinds of cancer? Read on to find out.
False Negatives and False Positives With Imaging Tests
Despite their usefulness, imaging tests aren’t perfect. Some can give us false negative results, while others can give us false positive results. We’ll discuss both of these possibilities next.
In recent years, thanks largely to advances in molecular biology, doctors have developed new blood tests that specifically target various proteins produced by cancerous cells. These markers, called tumor markers, offer a way around the limitations of standard imaging techniques. Tumor marker studies involve injecting patients with radioactive tracers, then scanning them with positron emission tomography (PET). With this method, researchers can determine where in the body the tracer is concentrated. If it accumulates in a particular area, perhaps indicating cancer, then further testing is warranted.
Unfortunately, not all tumors express tumor markers. Sometimes, a marker appears only after cancer spreads elsewhere in the body. Even if a tumor marker is present, however, its presence alone doesn’t confirm that cancer exists. For example, a woman whose breast tissue exhibits high levels of HER2/neu receptors may test positive for the presence of cancer, but she may not actually have cancer. HER2/neu is found in healthy human tissues too, so elevated receptor levels can lead to false positives. Another pitfall is that some types of treatment, such as chemotherapy, can affect tumor marker production.
As a result, physicians must consider multiple factors before making a diagnosis based solely on tumor markers. First, they should check for abnormal levels of tumor markers in conjunction with clinical findings. Then they should take into account whether treatments used to raise the marker level had any effect on the actual condition being diagnosed. Finally, they should use other imaging methods, such as MRI, ultrasound and PET to support their decision.
Now let’s talk about another potential pitfall of imaging tests, false positives. False positives occur when a person receives a positive result on an imaging test despite no evidence of cancer. There are several reasons why this happens. One reason is that some conditions can mimic cancer. For example, a person with irritable bowel syndrome may get a false positive on an endoscopy performed to evaluate possible ulcers. Similarly, a man with prostate enlargement may draw attention away from his cancer by causing swelling and discomfort in his scrotum.
Other causes of false positives include errors made by technicians performing the test, differences in equipment between sites, misinterpretation of results, and incorrect interpretation of images. Because of these pitfalls, it’s important to consult your doctor whenever you’ve received a positive result on an imaging test.
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It’s easy to see how a test could mistakenly diagnose a noncancerous growth as cancer. For example, an osteoporosis screening could indicate a fracture in a vertebra, while a mammogram could wrongly suggest breast cancer. Both of these scenarios would prompt a biopsy, leading to unnecessary surgery. Fortunately, technological advancements mean that today’s imaging tests are much more accurate than ever, and they provide valuable data to help make a cancer diagnosis.
With the right combination of clinical evaluation, radiologic assessment and histopathology, cancer can be accurately detected and treated. However, without careful analysis, a patient may undergo unwarranted surgery or radiation therapy. Today’s advanced medical technologies allow cancer detection to be improved through minimally invasive approaches, increasing the likelihood that cancer will be identified and treated successfully.
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