Cancer incidence in persons with elevated cobalamin levels

BACKGROUND: Elevated cobalamin level (ECL) is an epiphenomenon for several cancer types. The clinical significance of ECL at routine testing is, however, unknown. The aim of this study was to examine cancer incidences among persons with ECL. DESIGN: In a cohort study, Funen County residents (inhabitants 476,580), Denmark, without cancer or injected cobalamin prescriptions were followed from first cobalamin measurement during 1999-2009. Follow-up was stratified according to age, gender, and whether the cobalamin level was elevated (> 1,200 pmol/L). Data from national registers on age-specific incidence of cancer in the general population were used to calculate standardised morbidity ratio (SMR). RESULTS: A total of 490 persons with ECL and 40,104 with non-ECL were followed. Median age was 61 [IQR 44-77] years. Average follow-up was 2.0 years for ECL subjects and 2.7 years for non-ECL subjects. Cancer was diagnosed within the first 6 months of follow-up in 6.7% (CI 4.7-9.3) of ECL subjects and 2.6% (CI 2.4-2.7) of non-ECL subjects. In ECL and non-ECL subjects, SMR for cancer diagnoses were 15.1 (CI 10.4-21.2) and 5.0 (CI 4.7-5.3) within the first 6 months and 3.7 (CI 1.4-8.1) and 1.8 (CI 1.6-2.0) in the following six-month interval. Review of medical records revealed a suspicion of cancer or performance of relevant diagnostic tests in 87% at the time of cobalamin measurement. CONCLUSIONS: Persons with ECL have a high incidence of cancer partly explained by the reasons for measuring cobalamin. It remains to be determined whether accidentally found ECL would justify a search for cancers.