A large sample size is needed to find one case of cancer caused by contaminated valsartan - FDA reports
I read with great interest this Danish nationwide cohort study by Pottegård and his colleagues (1), in which they investigated whether the use of N-nitrosodimethylamine (NDMA) contaminated valsartan products is associated with the risk of cancer in Danes.
It should be noted that, in an updated official report from FDA (2) related to contaminated valsartan, FDA scientists estimated that one additional case of cancer may be found among eight thousand people who keep taking the highest contaminated valsartan dose every day for the full four year. This claim gives us an intuitive impression that the risk of cancer caused by the problematic valsartan is extremely minimal. Given only 6000+ subjects who had taken this contaminated drug in the last 4.6 years were included this cohort study, I am afraid that this sample size seems far from big enough to detect the hypothesized association in this study.
Furthermore, I noticed that Pottegård and his colleagues (1) only adjusted the covariates including age, sex, medication history and disease-related factors in their study. In this case, potential bias would likely to be introduced because of many other well-known important covariates that were unadjusted such as patients lifestyle (smoking, alcohol et al.) and other environmental factors (eg. occupation-related exposure). These confounders can largely distort and even reverse the association between contaminated valsartan and cancer, especially when the association is assumed to be extremely low.
In conclusion, the interpretation of the results from this study should be done with caution.
1. Pottegård A, Kristensen KB, Ernst MT, Johansen NB, Quartarolo P, Hallas J. Use of N-nitrosodimethylamine (NDMA) contaminated valsartan products and risk of cancer: Danish nationwide cohort study. BMJ 2018; 362 doi: https://doi.org/10.1136/bmj.k3851.
Competing interests: No competing interests