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Reduction in numbers of the macrophages caused by alendronate renders anti-inflammatory treatment redundant.Our findings on colon cancers raise the question of possible effects on other gastrointestinal cancers. For example, there has been considerable publicity related to recent reports of a possible link between use of bisphosphonates and oesophageal cancer [42]. We found no evidence for such a link when we analysed national health care data from Denmark [43]. Moreover, there was even a trend towards a reduction in gastric cancer. Other recent reports from UK [17] and USA [44] support our observations of the lack of an association between bisphosphonate use and oesophageal cancer. Furthermore, in contrast to colon cancer, it is harder to envisage plausible mechanisms to explain such an association [45]Strength sof the studyThe long-term data based on prescriptions from hospitals, general practices and private clinics from the entire country (Denmark), with outcome data from the cause of death register and hospital discharge diagnoses, and the size of the study are the main strengths. The time to effect and the relationship to the cumulative exposure to alendronate, with near significant reductions in risk in patients who take more than 180 DDD compared to users with low exposure, suggests a true biological effect rather than allocation bias. Our alendronate cohort and the four times as big control cohort, followed formorethan 100,000 patient years, provides our study with a statistical power that for most clinical trials would take 20–30 years to achieve.Limitations of the study
This was an observational study and, therefore, causality cannot be assumed. Although we adjusted for most of the established risk factors, confounders such as levels of 25 (OH) D or use of vitamin D and/ or calcium supplementation were not available for analysis. Despite biological plausibility, the Institute of Medicine (IOM) committee concluded recently that “ the evidence that vitamin D reduces cancer incidence and related mortality was inconsistent and in conclusive as to causality” [46]. In our study, it is likely that the bisphosphonate users were taking vitamin D and calcium supplements as part of the routine recommendations for osteoporosis treatment. This exposure was in the form of over-the-counter medications, which cannot be monitored.
We cannot exclude the possibility that more bisphosphonate users than non-users underwent early diagnostic procedures that led to the diagnosis of cancer at a less advanced stage. If so, this could bias post-diagnosis survival time towards longer survival time, but would bias incidence rates towards an increase and not a decrease, as was a key finding in the current study. It is possible that some subjects (in both arms) could have received bisphosphonates prior to the establishment of the NPD in 1995. This would bias estimates conservatively.
In conclusion, the risk of cancer deaths, and in particular death caused by colon cancer, is lower in
patients treated with alendronate, with survival curves deviating progressively after 2 years. There were excess pulmonary disease deaths in alendronate-treated patients— this is not unexpected as glucocorticoid use and smoking are strong risk factors for osteoporosis— but this did not account for the reduction in colon cancers.
The effects appear to be quite remarkable, but this was not a randomised study and unmeasured confounders could have influenced the results. Additional research is needed to establish whether this reduced mortality can be verified and its likely mechanisms. Following the discovery of the biological effects of bisphosphonates around 40 years ago [47], their major use has been to reduce excessive bone resorption. However, when given with food, alendronate and other bisphosphonates are virtually non-absorbed, so their skeletal effects are minimised. If these effects on colon cancer are confirmed, it is conceivable that bisphosphonates might be adapted for use in the chemoprevention of colon cancer.
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