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Cancer Screening: Everything You Need To Know About Early Cancer Detection

by — 2020-02-04 in Cancer
Millions of patients lose their lives to cancer every year. Tests that can discover cancer in its earlier stages are more widely available than ever, and the results tell us many of these deaths could have been avoided with the right kind of prevention.

Cancer is the second leading cause of death in the world, preceded only by heart disease. Because people live longer now, but they’re  also still exposed to various risk factors, it is only a matter of time before cancer claims the top spot on this infamous list. In fact, new studies have already found this to be somewhat true, because in some high-income countries —  like Sweden, Canada, and Turkey — more people die from cancer than cardiovascular diseases.

Although lung cancer is the most common cancer diagnosis across the board, there are differences between the sexes. Other than lung cancer, men most commonly get diagnosed with prostate and colorectal (bowel) cancer. In women, however, breast cancer is the most common cancer diagnosis, followed by colorectal and lung cancer. Cervical cancer, while taking the fourth spot overall on this list, is the top cause of cancer deaths in less developed countries.

As grim as all that sounds, we are not completely powerless against cancer.

For example, a large amount of deaths from cancer can be evaded by leading a healthy lifestyle and avoiding known cancer risk factors such as smoking, obesity, and alcohol abuse. Vaccines designed to prevent some infections that can lead to cancer, like Hepatitis B as a cause of liver cancer, and the human papilloma virus (HPV) when talking about cervical cancer, have also emerged. These measures to prevent you from falling victim to cancer in the first place are all forms of primary prevention.

On the other side, a large number of cancers have high cure rates if they are detected in their early stages. Early diagnosis significantly reduces death rates from a specific disease, and sometimes even decreases the number of newly diseased patients when problems are caught in the precancerous stage. This is known as secondary prevention.

Types of preventable cancers include:

  • Breast cancer
  • Cervical cancer
  • Colorectal cancer
  • Lung cancer
  • Prostate cancer
  • Melanoma (skin cancer) 

What is cancer screening?

Screening is a form of secondary prevention that uses various medical tests with the goal of catching a specific disease early on, even before symptoms arise. As you’ve already noticed, the most common cancer types belong to the “preventable” category. It is for that reason that standardized screening strategies were developed to combat cancer.

These strategies encompass certain tests, which can be applied:

  • To all individuals belonging to a certain population – called mass or universal screening. The recommendation for screening is usually based on biological sex or age.
  • Smaller groups within the same high-risk population – this is called selective screening and it can be applied more selectively, such as to families and people within certain professions.
  • Or even individuals – opportunistic screening.

Besides population, there are other strict criteria to be met when organizing a screening program.

First, the disease must present a serious public health issue. Other than that, the natural course of the disease must be fully understood, because only curable diseases with a presymptomatic phase may be screened for.

The test used for screening must be simple, quick, safe, precise, and sensitive for the specific disease. Also, the test mustn’t be expensive, which helps the screening program maintain its cost-benefit ratio. Because screening is a continuous process, funds are necessary to achieve both the screening itself and adequate follow-up methods for the treatment of patients with a positive diagnosis.

It is important to mention that not all screening programs are perfect, so the results may sometimes be false positives or false negatives. Therefore, it is essential to choose the method with the highest proven accuracy rate.

What types of tests do cancer screening programs involve?

The risk of cervical cancer can be detected using the Papanicolaou (or Pap) test, in which a gynecologist collects cervical cells and subsequently views them under the microscope to detect potential abnormalities. The goal population for Pap smears includes all females from 25 to 64 years old. If two Pap tests are shown to be negative a year apart, further checks are recommended only once every three years.

Colorectal (bowel) cancer can be screened for during a colonoscopy where polyps may be found. Because this type of cancer develops from polyps, they should subsequently be removed.

However, due to the invasive nature of colonoscopy, some medical associations recommend the so-called FOB (fecal occult blood) test, which can detect microscopic amounts of blood in feces. Since blood finds its way into the stool from other causes than cancer, meanwhile, people with a positive FOB test should be sent to colonoscopy for a definitive diagnosis. The goal population here includes all people over 50, and the test should be done once every two years.

Prostate cancer is screened for via a blood test called the PSA (Prostate specific antigen) test, which measures the concentration of a hormone used as a tumor marker for prostate cancer. Unfortunately, because there is no firm evidence that this type of screening can reduce the death rate associated with prostate cancer, this type of screening program is not available in many countries. However, men over 50 years old should have their PSA levels checked at least once a year.

Melanoma (a type of skin cancer), is routinely checked for by dermatologists.

Breast cancer can be detected using mammography, a low-dose X-ray-based imaging method used to diagnose small changes in the breast which can not be discovered via other types of examinations. The mammogram is a rectangle-shaped box. During this examination, the breast is placed inside the mammogram and firmly pressed, which can be a bit uncomfortable.

Next, every breast is filmed separately, and the results are then discussed. Because mammography is a very subjective method, two different radiologists usually review the same patient, thereby minimizing the risk of misdiagnosis. The goal population for mammography includes all women over 50, and the process should be carried out once every two years.

Unfortunately, mammography is not as effective as a breast cancer screening method in the younger population. This is because the risks outweigh the benefits, mostly because of ionizing radiation and the varying number of false positive and negative results caused mainly by different breast densities or the subjectivity of the interpretations.

If there are any potential issues, the patient is subsequently sent to undergo other imaging methods, including a breast ultrasound, or to a lesser extent – a breast MRI.

*Note that all of the mentioned populations and tests may vary from country to country, and even from medical center to medical center. The examples given include the most common protocols used to screen for cancer.

What role does diagnostic imaging play in cancer screening?

The expansion of new technology in medicine, especially in radiology, makes imaging methods more valuable today than ever. In fact, three out of four most common types of cancer (breast, lung, and colorectal) are already being screened for successfully via imaging methods.

  • Breast cancer screening is evolving, and 3D mammography is now possible thanks to technologies such as CT, MRI, and PET/CT hybrid scans. The use of this technology in the future will help detect new breast cancer cases which can’t be seen using contemporary mammography.
  • Lung cancer screening uses special protocol low-dose CT (LDCT) scans to diagnose lung abnormalities before they have the chance to evolve into something more sinister. The population being screened includes long-term smokers between the ages of 55 and 77. That way, the patient can undergo treatment on time, showing this method to be literally life-saving.
  • Colon cancer screening can be done via a special method called CT colonography (CTC), which basically acts as a virtual colonoscopy. This colon cancer screening method is not as invasive as a regular colonoscopy, although certain preparations are needed for the exam to be carried out. For example, you will be instructed to clear your bowels before the test, and take medications if you are allergic to contrast agents.
  • Prostate cancer screening with the help of imaging tools is still in its infancy, primarily due to its relative high price. However, studies are now being performed using MRI to detect changes in the population with high PSA test results, and it has been shown that MRI can outperform PSA tests as a reliable predicting tool in prostate cancer screening.
The general problem with these new imaging screening methods is that they are currently very expensive, so mass screenings aren’t yet recommended. Also, the potential risks of ionizing radiation are too high for the general public. Until these problems are solved, medical imaging tools such as CT and MRI will primarily be helpful in the process of staging an already diagnosed cancer, as well as a useful tool for cancer biopsies. In the meantime, we would recommend that you participate in any cancer screening programs for which you are eligible.

Sources & Links

  • Photo courtesy of SteadyHealth

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