It is impossible for today's detection methods to determine where mutated and/or cancer cells are located in the body. In order to detect cancer, scientists have been limited to testing samples of blood or saliva for specific biological markers that correlate with the presence of cancer cells anywhere in the body. Once detected, a biopsy must be performed to determine if cancerous cells are invading healthy tissue.
The detection process, therefore, requires two invasive procedures: first a test to determine whether cancer is present, and then a biopsy to confirm the presence of cancerous tissue. This is akin to finding a needle in a haystack: before you know for certain if the needle exists, you need to search through all the hay.
To detect cancer in its early stages, when it is most easily treated and cured, requires an earlier diagnosis. But this comes with significant caveats: the test must be able to distinguish between healthy cells and cancerous or pre-cancerous cells before they become visibly abnormal or symptomatic. Since researchers have yet to discover a foolproof biological marker that can identify cancer cells, there is currently no such test available.
Early cancer detection is thus limited to that determined by medical imaging, which detects physical abnormalities. Similarly, there is no test that can determine the location of cancerous cells in the body. While there are some biological markers able to indicate their presence, they cannot pinpoint where in the body they are located.
Cancer cells share many common traits with healthy, normal cells. The only way to be sure that an abnormality is caused by cancerous cells is for a pathologist to look at the cell structure histologically and confirm that the cells are malignant (cancerous). The only ways to get this information are through surgery or biopsy.
Preliminary tests that show promise for detecting cancer without invasive procedures include:
Most current detection methods are based on identifying known biological markers for cancer, which have to be present in abnormally high numbers before they can indicate the presence of cancer. These tests are subject to false positives because other conditions may elevate marker levels. The same holds true for screening tests looking for
early signs of cancer in healthy people. An elevated marker level is not definitive proof of cancer. Further biological testing is required to make an accurate diagnosis.
It is important to note that, while there are many screening tests for various cancers available, there is no test that can detect all forms of cancer with equal accuracy.
Cancer screenings are usually administered by a primary care physician or specialists such as a general oncologist or gynecological oncologist.
The National Cancer Institute recommends some cancer screening tests depending on the patient age, gender, and family history. These are generally given once a year.