One-year cancer risk after detection of blast cells in peripheral blood.

Haematologists are often consulted on the need for additional diagnostic workup in patients with blast cells in peripheral blood. However, cancer risk (including solid tumors) after detection of blast cells in peripheral blood is lacking. Therefore we evaluated the 1-year cancer risk following detection of blast cells in peripheral blood. We used population-based retrospective data from the Region of Southern Denmark (2014-2021), including 2,187 individuals aged ≥20 years with blast cells in blood samples, excluding those with prior cancer. Results from haematological parameters derived from the laboratory information system, while diagnoses and vital status were from administrative registers. Natural language processing assisted review of clinical notes for individuals without cancer codes. We estimated age-standardised cancer incidence rates and compared observed versus expected cancers using standardised incidence ratios (SIR). We found that the overall 1-year cancer risk was 23% [95% CI: 21-24], with 19% [95% CI: 18-21] for haematological cancers and 3% [95% CI: 2-3] for solid cancers, compared to 0.87% in the background population. The age-adjusted SIR was 22 [95% CI: 21-24] and was highest for haematological cancers at 199 [95% CI: 184-214]. Although 78% of individuals had no blast cells upon repeated testing, 27% still developed cancer within a year. In conclusion the presence of blast cells in peripheral blood may warrant consideration of further diagnostic evaluation, particularly in the presence of other haematological abnormalities.