How Accurate Are Blood Tests for Cancer?

While cancer remains a leading cause of death in the U.S., claiming more than 500,000 lives each year, advances in medical science are improving patient prognoses all the time. In the mid-1970s, the National Cancer Institute (NCI) reported that only 50% of cancer patients survived beyond five years. From 2005 to 2011, that number increased to nearly 67%. While new and innovative treatments are increasing cancer patients’ lifespans, early detection remains critical. Unfortunately, there are many cases where growths and tumors go undetected until it is already too late – even when bloodwork has already been performed. In this article, our missed diagnosis attorneys will compare the accuracy rates of some common blood tests for cancer.

Which Blood Tests Are Used to Diagnose Cancer? How Accurate Are They?

Scientists can use genetic markers, which are genes or part of DNA sequences with fixed locations on certain chromosomes, to identify species or even individuals. Tumor markers are substances – typically but not always proteins – which are produced by cells in response to cancer, and therefore, tend to be present in elevated levels in cancer patients. Some examples of tumor marker blood tests for different types of cancer include:

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Breast Cancer – CA15-3/CA27.29 blood test

  • According to a study published in Clinical Chemistry, “CA27.29 discriminates primary breast cancer from healthy subjects better than CA15.3, especially in patients with limited disease.”

Colorectal Cancer (Colon Cancer) – CEA (Carcinoembryonic antigen) blood test

  • CEA levels become increasingly detectable as colorectal cancer progresses. According to a 2006 article published in Oncology, “In a study of 358 patients who presented to surgery with a diagnosis of colon cancer, only 4% of patients with stage I disease had an elevated CEA… whereas 25%, 44%, and 65% of patients with stage II, III, and IV disease, respectively, had abnormal levels.”

Liver Cancer – AFP (Alpha-fetoprotein) blood test

  • Unfortunately, the sensitivity and efficacy of AFP tests has been called into question by many scientists. As a 2005 study in Oxford medical journal HPB pointed out, “AFP used alone can be helpful if levels are markedly elevated, which occurs in fewer than half of cases at time of diagnosis [of hepatocellular carcinoma, the most common type of liver cancer].”

Lung Cancer – Cytokeratin fragment 21-1 (CYFRA 21-1) blood test
A 2005 study in The Oncologist compared several different methodologies for testing for lung cancer, and found CYFRA 21-1 blood tests to perform slightly worse than alternatives like CA 15-3. “CYFRA 21-1 was assayed in five reports,” the study stated. “Two found it to be the best tumor marker of malignant pleural effusion… and, in three studies, it was second to other markers. Our findings agree with the latter reports.” (Pleural effusion, or a build-up of fluid between the chest and lungs, is commonly caused by lung cancer.)

Other Methods of Detecting and Diagnosing Breast, Lung, and Colon Cancer

Elevated levels of tumor markers do not always mean that a person has cancer, because they can also be caused by many other non-cancerous medical conditions. However, because tumor markers are a major indicator of cancer, a doctor who finds elevated tumor markers in a patient may call for a biopsy (tissue sample analysis), an x-ray, or other types of lab tests to confirm possible presence of cancer. These tests might include:

Breast Cancer

  • Mammograms – According to the NCI, mammograms detect breast cancer in about 80% of screenings. That leaves a huge rate of false negatives: nearly one fifth of all breast cancer patients who receive mammograms. Other tests for breast cancer include breast ultrasounds, MRIs, and biopsies.

Colorectal Cancer

  • Colonoscopy – Colonoscopies have a high accuracy rate, missing colon cancer only 5% of the time according to a study published this year in Annals of Gastroenterology. However, while colonoscopies are usually successful in detecting colorectal cancer, the small number of false negatives means that patients who are worried about colon cancer should consider undergoing additional tests for confirmation of initial colonoscopy findings. Other types of tests for colon cancer include sigmoidoscopies and Fecal Occult Blood Tests (FOBT).

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Lung Cancer

  • Chest X-Ray – According to a 2006 study in the British Journal of General Practice, chest x-rays of patients with lung cancer turn up false negatives nearly 25% of the time. In light of this alarming miss rate, patients who are worried about lung cancer may want to ask for additional tests, such as a sputum cytology, where a sample of sputum (phlegm) is examined under a microscope for the presence of lung cancer cells. A 2013 study published in Chest described sputum cytology as an “acceptable method of establishing the diagnosis of lung cancer,” noting a sensitivity rate of 66% and a specificity rate of 99%. (Sensitivity refers to the number of correct positive diagnoses, while specificity denotes the number of correct negative diagnoses.)

If a blood test or other lab test missed your cancer diagnosis, you may be entitled to compensation. While compensation cannot undo the lab’s mistake, it can help keep you and your family more comfortable as you go through this difficult time together, providing financially for both the present and future. To set up a free, completely private legal consultation, call the clinical malpractice lawyers of Whitney, LLP at (410) 583-8000.


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