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ASSOCIATION OF NATURAL KILLER CELLS ACTIVITY WITH THE INCIDENCE 
OF COLORECTAL NEOPLASIA AT SCREENING

Relevance: Increased natural killer cells (NK cells) activity is associated with reduced colorectal cancer (CRC) risk. Previously published 
studies examined the association of NK cells and CRC prevalence in individuals at high cancer risk. 
The purpose was to study the relationship between NK cell activity and the incidence of advanced adenomas (AA) and CRC in a population 
with average cancer risk. 
Methods: The activity of NK cells was assessed by enzyme immunoassay (ELISA) of blood in participants of average risk with a measurement 
range of 25-2500 pg/ml. The level of NK cells below 200 pg/ml was defined as pathological. The informativeness of the diagnostic test for determining NK cell activity was assessed using indicators such as sensitivity, specificity, negative and positive predictive value, and clinical utility index. 
The probability coefficient for the development of colorectal cancer was calculated using logistic regression. 
Results: The activity of NK cells was assessed in 354 persons of average risk (mean age 59 years; 36% of them men). The diagnostic accuracy 
of NK cells determination for CRC and AA was 76% and 72%, respectively, and the negative predictive value was 96%. The NK cell test demonstrated a good negative clinical utility index for CRC and AA (0.66 and 0.74, respectively). Individuals with low levels of NK cells were seven times 
more likely to be diagnosed with CRC (95% CI 2.3-20.3; p<0.001). NK cell levels were higher in men compared to women (549 pg/mL vs 500 pg/ 
mL) and lower in smokers (412 pg/mL versus 544 pg/mL), non-athletic participants (413 pg/mL versus 654 pg / ml), in people who abuse alcohol 
(389 pg/ml versus 476 pg/ml). 
Conclusion: Our study shows that a high level of NK cells can potentially exclude CRC and AA in individuals with average cancer risk