Routine Primary Care Blood Testing for Gastric Cancer Detection

Gastric cancer is the 5th most common cancer worldwide, impacting over 1 million people with new diagnoses each year. Unfortunately, gastric malignancy often has a poor prognosis by time it is diagnosed, which is usually in its more advanced stages. This greatly decreases the overall 5-year survival rate for this disease to only 36%. The relatively high prevalence of this cancer coupled with its extremely low survival rates beg the question: what can be done to increase detection of gastric cancer in earlier, more treatable points in its disease course?

Nonspecific Symptoms of Gastric Cancer

A major part of the challenge in diagnosing gastric cancer is that patients with early stage disease can be asymptomatic. If they do have symptoms, the symptoms are often vague and are therefore easily mistaken for benign GI conditions. Some of the early signs of gastric cancer include:

• Nausea and/or vomiting
• Changes in appetite patterns
• Abdominal pain or discomfort
• Early feelings of fullness
• Heartburn
• Indigestion

Why is Everyone Not Tested?

The major problem here seems to lie in the fact that testing for cancer is never a first line option when working up a patient with non-specific GI symptoms. With the previous information in mind, you may be wondering: why is everyone with GI symptoms not tested for gastric cancer, if it is such a deadly disease? 

The answer is twofold. First of all, testing everyone for gastric cancer involves expensive imaging techniques and possibly invasive procedures. Unnecessary use of these methods would be a waste of costly resources, as the vast majority of patients with the above GI symptoms will not have cancer, but a much more routinely treatable condition. 

More importantly, testing everyone for gastric cancer would also do more harm than good for patients. Diagnostic tests require a high pretest probability in order to be most useful and accurate. Having a high pretest probability means that, based on already known evidence, there is already a high chance that a person actually has the condition we are testing for, in this case gastric cancer. Things that can increase this chance include symptoms, risk factors, medical history, and physical exam findings. In short, if you initially think someone likely has the disease, and a test comes back positive, that positive result is more trustworthy.

On the other hand, if someone with a low initial chance of having the disease is tested, the test results may be misleading. This could lead to false positives, where a test says the patient has the disease when they truly do not, or false negatives, where a test says the patient does not have the disease when they truly do. Evidently, both of these options would be problematic, with false positives causing unnecessary stress to the patient and false negatives potentially being catastrophic for their prognosis.

Importance of Early Detection and Use of Screening Tests

Despite this conundrum, the importance of early detection for gastric cancer patients remains a reality. In fact, the isolated 5-year survival rate for gastric cancer patients with only localized disease can be as high as 75%, which is over double the overall survival rate. This underscores the importance of finding a way to detect gastric cancer patients before their disease spreads. As previously mentioned, this cannot be done by performing diagnostic tests on every patient with non-specific GI symptoms. However, screening tests accomplish exactly this goal. 

Screening tests have a high true negative rate, meaning that they are great at ruling out disease. They are inexpensive, minimally invasive, and can be widely used. The problem is that, until this year, a reliable screening test for gastric cancer had not yet been developed.

Predictive Value of Routine Blood Tests

In late July of 2024, Rafiq et al. published a monumental study regarding screening in gastric cancer patients with nonspecific abdominal symptoms. Their idea was based on the fact that patients with the initial symptoms of gastric cancer will often first present to their primary care clinic. When seen by a primary care provider, these patients will often receive routine blood tests, including a complete blood count and analysis of inflammatory markers. Interestingly, the authors proposed using these blood tests to initially identify patients that may be at higher risk of gastric cancer for further testing.

Results showed high potential for this screening method, with several blood test results increasing the pretest probability of gastric cancer to beyond the threshold for specialist referral and further testing. An example of this is seen in the population of females aged 50-59, where the “pre-blood test cancer risk of 1.6% increased to: 10% with raised ferritin, 9% with low albumin, 8% with raised platelets, 6% with raised inflammatory markers, and 4% with anemia.” It was also found that, for every 1,000 patients presenting with the nonspecific symptom of bloating, use of blood tests would identify 3 additional patients with gastric cancer compared to the current method of risk assessment. This would translate to a 16% increase in gastric cancer diagnosis yield and potentially saved lives. 

Conclusions

Routine blood tests through a primary care provider may be the solution to a persistent dilemma of finding an appropriate screening method for the deadly disease of gastric cancer. Evaluation of blood test results in combination with the current risk assessment method can identify more patients with sufficient risk to undergo further testing. This can lead to more detections of gastric cancer prior to spread and drastically increase the survival rate if implemented as a standard protocol.

Summary

Gastric cancer often presents with vague symptoms and is typically diagnosed at advanced stages, leading to a poor prognosis and a low 5-year survival rate. Routine blood tests, such as analyzing inflammatory markers and complete blood count, have been proposed as a potential screening tool in primary care settings to identify higher-risk patients for further gastric cancer testing. A July 2024 study in PLOS Medicine demonstrated that these blood tests could significantly increase the pretest probability of gastric cancer, leading to earlier detection in certain patient populations. This method has a high potential to increase survival rates by diagnosing this deadly disease at earlier, more treatable stages.