The practice of medicine comes with tradeoffs. Most of risks associated with treatment are small, usually inconsequential and obvious during or immediately after the treatment is given. Cancer results from damage to genes involved in growth and regulation of cells. Growth regulatory systems have multiple damage control and backup pathways. The regulatory systems fail only after multiple hits. Years of exposure is required to carcinogens is needed to cause enough DNA damage for a cancer to emerge. Unlike other drug toxicity, the carcinogenic potential of a therapy may take years to manifest. The same can be said about heart disease which along with cancer is responsible for the largest disease burden in an ageing population.
I had earlier written about the protective effect of bisphosphonates in breast cancer. Within few years of introduction of oral bisphosphonates for the therapy of osteoporosis, it became clear that these agents carried a risk of oesophagitis and oesophageal perforation. About a decade later a concern about the association of oesophageal cancer emerged. A recently published study (BMJ 341:4444c; 2010) has concluded that the use of oral bisphosphonates increases the risk of oesophageal cancer. The study found that one (or more) prescription for oral bisphosphonates increased the risk of oesophageal cancer by 30%. Ten or more prescriptions nearly doubled the risk. Using the same database another study, with a shorter follow up, (JAMA304:657-63;2010) had failed to show an increased risk. Selective oestrogen receptor modifiers (tamoxifen and raloxifene) are used to treat osteoporosis and are effective in and under evaluation for chemoprevention of breast cancer. Tamoxifen increases the risk of endometrial cancer. Both increase the risk of thrombosis.
This is not the first time a therapy has been implicated in a serious adverse effect after years of use and this will not be the last. Intervention in chronic disease improves the health of ageing population. A chronic disease also provides a large market for the pharmaceutical industry. It is for the medical community to recognize that there are tradeoffs in medical practice. As we treat an aging population the need becomes more acute.