A screening test is a diagnostic test that is performed on healthy individuals to rule out the possibility of disease. Cancer screening, specifically, is a group of tests that are performed on healthy individuals to check for the presence of cancer. Cancer screening is performed even when individuals do not feel any signs or symptoms related to the possibility of cancer. These tests are often performed routinely as part of the wellness check-up of an individual.
Candidates for cancer screening
There are two main types of cancer screening: general cancer screening and selective cancer screening.
General cancer screening is done for all individuals who fall within the criteria for a particular cancer screening test. The criteria are usually based on gender and/or sex. For example, general cancer screening for breast cancer recommends that all females who are 40 years old and older should have yearly mammogram to check for breast cancer.
Selective cancer screening, on the other hand, is a more directed type of cancer screening that is done on individuals who have identified risk factors for a particular type of cancer. Selective cancer screening is usually performed earlier (or on younger individuals) and sometimes employ more invasive diagnostic tests because of a higher index of suspicion. For example, individuals with first degree relatives who have BRCA gene mutation are advised to have yearly mammogram starting at 30 years old (compared to the 40 years old standard on the general population).
Benefits of Cancer Screening
Cancer screening will not improve the health of an individual, but it will give that individual a better chance to fight cancer if it is indeed present. Cancer screening allows for early detection of cancer; it identifies cancer even before it creates telltale signs and symptoms. Cancer screening aims to identify tumors while they are yet a few millimeters to a few centimeters in size. Detecting cancer in its early stage allows for better management, better treatment options, and even higher percentage of cure. In contrast, late-stage cancers are generally associated with poorer prognoses, limited treatment options, and lesser chances of cure. In early-stage cancer, the general aim is for cure whereas in late-stage cancer, the aim is sometimes just for palliation.
Screening for different types of cancer
The guidelines for the different types of cancer screening can vary with location, race, and the society providing the recommendation. The following are the general recommendations for cancer screening by the American Cancer Society:
- Breast Cancer - Aside from the regular monthly self-breast examination, screening for breast cancer is done by performing a yearly mammogram, which is recommended to be started at the age of 40. The frequency of screening can be decreased to every two years at the age of 55.
- Colorectal cancer - Individuals aged 50 or older are recommended to have any of the following procedures to screen for colorectal cancer:
- Colonoscopy should be done every 10 years. Colonoscopy involves insertion of a scope through the anus (under anesthesia or sedation) to visualize the entire colon.
- Sigmoidoscopy should be done every 5 years. Sigmoidoscopy is just like colonoscopy except that it has a shorter range of coverage and visualizes only up to the sigmoid colon.
- Double contrast barium enema should be done every 5 years. Double contrast barium enema involves taking x-rays of the colon after it has been filled with barium and air.
- CT scan of the abdomen (CT colonography) should be done every 5 years.
- Fecal occult blood test (FOBT) should be done every year. FOBT is an examination that detects blood in the stools.
- Cervical Cancer - Women aged 21 and above should get a Pap smear every three years to screen for cervical cancer. A pap smear is done by getting a swab from the cervix and looking at the sample under the microscope to detect for the presence of abnormal cells. Women who are aged 65 and who have tested normal for Pap smear for 10 consecutive years may discontinue screening for cervical cancer.
- Lung Cancer - Screening for lung cancer is done using a low-dose chest CT scan. However, this is not recommended for the general population. Lung cancer screening is recommended only for those selected individuals who are at high risk for developing lung cancer like the heavy chain-smokers.
- Prostate Cancer - Screening for prostate cancer is done by measuring the levels of Prostate Specific Antigen (PSA) in the blood. However, this test is not recommended for the general population, and men are advised to consult personally with their doctors to know if it is indicated for them.
Tumor markers are naturally occurring substances or biomarkers in the blood that can be measured to detect the presence of a specific tumor. The levels of tumor markers in the blood can become elevated in proportion to the activity of the cancer process. Tests for tumor marker are requested by physicians (oncologists) to aid in the diagnosis of certain types of cancers. It is also common to measure the levels of these markers before and after treatment to document the adequacy of treatment and to monitor for the recurrence of the disease. Some examples of these tumor markers are:
- Prostate Specific Antigen (PSA) for prostate cancer
- Alpha-Feto Protein (AFP) for liver cancer
- Carcino-Embryonic Antigen (CEA) for colon cancer
- CA 125 for ovarian cancer
- CA 19-9 for pancreatic cancer