An elevated platelet count is associated with an increased risk of several types of cancer, according to research published in JAMA Network Open.
Researchers noted that the association was “transient and attenuated with increasing time” from the complete blood count (CBC) test to the date of cancer diagnosis.
“Overall, given the transient nature of the association with platelet count, our findings suggest that an elevated platelet count detected through routine blood examination may be a consequence of the presence of cancer rather than being a risk factor for the disease,” the researchers wrote.
For this study, the researchers looked at 8.9 million eligible Ontario residents who had a routine CBC test performed from 2007 through 2017. More than half of the cohort (55.8%) were women, and the median age at the first CBC test was 46.4 years.
In all, 5.6% of patients were diagnosed with a first primary cancer during the observation period. The median observation time was 7.3 years (range, 4.4-9.3 years).
For blood samples taken in the 6-month period before diagnosis, patients with a very high platelet count (≥90th percentile) had more than double the risk of a solid tumor diagnosis (odds ratio [OR], 2.32), compared with patients who had a medium platelet count (>25th to <75th percentile).
The OR for this association decreased with increasing time from the CBC test to cancer diagnosis. The OR for patients with a very high platelet count decreased to 1.41 for the period from 6 months to 12 months before diagnosis.
For the 0- to 6-month period before a cancer diagnosis, a very high platelet count was associated with an increased risk of colon cancer (OR, 4.38), lung cancer (OR, 4.37), ovarian cancer (OR, 4.62), stomach cancer (OR, 4.27), esophageal cancer (OR, 3.18), other gastrointestinal tract cancers (OR, 3.10), and kidney cancer (OR, 2.55).
“For several cancer sites (lung, colon, stomach, esophagus, and kidney), a high platelet count was associated with a cancer diagnosis in the following 3 or more years,” the researchers wrote. “For lung cancer, a significant association was present 10 years before diagnosis. Long-term associations were also seen for kidney cancer and esophageal cancer.”
According to the researchers, various mechanisms may be responsible for the association between high platelet count and cancer, including “the aggregation of cancer cells by platelets, increased extravasation or enhanced permeability of the basement membrane, and shielding cancer cells from immune attack in the bloodstream.”
The researchers plan to conduct additional studies to assess the utility of platelet count as a screening test for cancers.
Giannakeas V, Kotsopoulos J, Cheung MC, et al. Analysis of platelet count and new cancer diagnosis over a 10-year period. JAMA Netw Open. Published online January 11, 2022. doi:10.1001/jamanetworkopen.2021.41633