Today, we take a brief look at how researchers in Ontario (Canada) are opening the door to using a simple blood test to help determine the cancer risk for an individual.

Platelets 101

What are platelets? Marlene Williams, M.D., director of the Coronary Care Unit at Johns Hopkins Bayview Medical Center, offers this excellent explanation:

“Platelets are the cells that circulate within our blood and bind together when they recognize damaged blood vessels.”

She continues: “When you get a cut, for example, the platelets bind to the site of the damaged vessel, thereby causing a blood clot. There’s an evolutionary reason why they’re there. It’s to stop us from bleeding.”

When I think about the relationship between cancer and platelets, it is usually in the context of anti-cancer treatment. For example, low platelet counts (thrombo-cytopenia — THROM-bo-sigh-toe-PEE-ne-ah) can result from chemotherapy damaging the bone marrow reducing platelet production. Such injury is usually temporary.

Lymphoma and the blood cancer known as leukemia can invade the bone marrow. When the cancer cells occupy significant volumes of the marrow, an individual can have challenges making the platelets that they need.

Types of thrombocytopenia (low platelet count)

The Cleveland Clinic (USA) explains that there are three main classes of thrombocytopenia, including:

• Platelet destruction (such as an auto-antibody attached to the platelet surface).
• Platelet sequestration (isolation), for example, in an enlarged liver or spleen.
• Decreased platelet production associated with certain bone marrow diseases.

Platelets and cancer

Researchers analyzed data from nearly nine million Ontario residents to better understand the relationship between platelet levels and cancer risk. The subjects were enrolled in the provincial health insurance plan and had a routine complete blood count test between 2007 and 2017.

The Canadian researchers matched each patient with cancer to three controls (individuals without a cancer diagnosis) according to age, sex, and healthcare use patterns.

The scientists then calculated the cancer risk associated with each category of platelet counts at intervals up to ten years after a blood test.

Here are the odds ratios for those very high platelet counts. For example, an odds ratio of 4.6 means that those with very high platelet levels had a 4.6-times higher risk of getting ovarian cancer.

Study author Giannakeas observes that “the differences in our findings by cancer type surprised me.” He adds, “Clearly, there is a mechanism on platelets occurring with certain cancer types but not with others, such as breast and prostate cancer.”

The increase in relative risk appeared most pronounced for ovarian, lung, kidney, and gastrointestinal cancers (including esophagus, stomach, colorectal, and other gastrointestinal cancers).

Platelets and cancer — My take

Is the elevation in platelets a marker for future cancer, or does it indicate the presence of a current malignancy? The increase in risk appeared most significant in the six months after diagnosing thrombocytosis (too many platelets) and decreased rapidly after that.

These findings suggest that increased platelets may be a marker for the presence of existing cancer, rather than a factor associated with increased cancer risk. Cancer may be causing the platelet increase. If the platelet increase were a marker for future cancer, instead of being associated with current cancer, the risk period would likely be longer than six months.

An elevated platelet count may someday serve (along with other screen tools) as a marker for the presence of some cancer type. Thank you for joining me today. Nothing actionable, but the results hint at a future approach using a simple and relatively inexpensive blood test.

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