Why are certain cancers so hard to diagnose?

Why are certain cancers so hard to diagnose?
Medical science has made tremendous strides in the diagnosis and treatment of cancer.  Screening tests including mammograms for breast cancer, Pap smears for cervical cancer, and colonoscopies for colon cancer have allowed these cancers to be detected at an earlier stage when treatment is generally more effective. Treatment of several types of cancer including breast, testicular, skin and colon, if started early in their course, can result in a “cure” in a high percentage of cases.  Also, many people whose risk of developing cancer is increased can be identified by assessing risk factors, exploring family history or performing genetic testing.

Despite these advances, there are certain types of cancer that defy diagnosis and often carry a particularly grim prognosis. Pancreatic, ovarian, and lung cancers fall into this category.  Reasons for a delay in the diagnosis of cancer include:

  • Inadequate access to medical care
  • Lack of noticeable signs or symptoms in the early stages of certain cancers
  • Failure to seek medical attention for signs or symptoms suggesting cancer
  • Delayed diagnosis because of cancer signs or symptoms mimicking another illness
  • Absence of effective screening tests for certain cancers
  • Cancers “hidden” in organs that are not easily examined

When the diagnosis is delayed, the likelihood of the cancer progressing to a more serious stage or spreading to other areas of the body increases. This typically results in poorer treatment outcomes and higher cancer-related mortality. Pancreatic cancer is a classic example of this. Fewer than 20% of patients with pancreatic cancer are diagnosed while the tumor is confined to the pancreas.  In cases in which the cancer has spread away from the pancreas at the time of diagnosis, only 1 patient in 100 remains living 5 years later.

What can be done to improve early detection?  All of the cancers mentioned above can be diagnosed through physical exams and medical tests such as CT scans, MRIs, blood tests and ultrasounds. The specific diagnostic tests will vary depending on the type of cancer.
 
In regard to ovarian cancer, two tests, the transvaginal ultrasound and a blood test called CA-125, have been used to detect ovarian cancer. Currently, however, they are not recommended as a screening test for women in the general population since they have not been shown to reduce mortality. Women are encouraged to report symptoms associated with ovarian cancer to their doctor for further evaluation. These symptoms include abdominal swelling or bloating (due to a mass or a buildup of fluid), pelvic pressure or abdominal pain, difficulty eating or feeling full quickly, and/or urinary symptoms (having to go urgently or often).

Approximately 85% of lung cancer develops in former or current smokers. Screening for lung cancer is also not recommended for the general population. In high risk individuals (adults aged 55 to 80 years who have a significant smoking history and currently smoke or have quit within the past 15 years), however, the US Preventive Services Task Force recommends annual screening for lung cancer with low-dose computed tomography (CT scan).
 
Pancreatic cancer remains one of the most deadly forms of cancer with very little improvement in mortality rate over the past several decades. There are two cancer “markers” that can be detected with blood tests (CA19-9 and CEA). These tests, however, are not consistently positive even when pancreatic cancer is present and are not recommended as a screening test. Typically only vague symptoms that could be associated with several different gastrointestinal conditions are present when pancreatic cancer is suspected. These include pain (usually abdominal or back pain), weight loss, jaundice (yellowing of the skin and eyes), loss of appetite, nausea, and changes in stool.

With most of these difficult-to-diagnose cancers it appears that the best way toward early diagnosis is to be aware of changes in your body and discuss any troubling signs or symptoms with your doctor. More often than not, these new complaints will have nothing to do with cancer and can be treated or will resolve on their own. When persistent symptoms suggest cancer, however, making the diagnosis as early into its course as possible can lead to a much improved outcome.

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Image: ©Shutterstock / Rido

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