Of 10,507 participants in the Copenhagen City Heart Study, 18 were found to have this variant. (The authors describe using the assay technique described by Baxter et al., which implies only an examination of sequencing traces — much less sensitive than some other detection techniques used e.g. by Lauw et al.) For overall survival of these individuals in the 17.6 years of follow-up, all 18 of these mutation carriers died. For comparison, an age-matched subset of 540 had only 348 die during this interval (64%) — this different was highly significance (p=0.00003).
Of these 18, 11 had no cancer at the time of blood sampling. 7 of these (63%) later developed some sort of cancer in the subsequent time period, compared to 129 out of 473 in the age-matched population (27%) — p=0.0001 for a difference.
Of the 18, 15 were known to have no myeloproliferative or other hemotologic cancer at the time of blood sampling. Two of these went on to develop myeloproliferative cancer (p=7*10^-22) and, in total, four went on to develop some type of hemotologic cancer (including the two with MPD), a significance of p=2*10^-32.
The authors conclude, “These results document that, in some cases, presence of the mutation precedes the clinical diagnosis of myeloproliferative cancer.” The authors also note that it is possible others of the 18 individuals had myeloproliferative disorders that had been undiagnosed or misdiagnosed, as they were not being studied with the specific intent of collecting data regarding myeloproliferative cancer.