A large new U.S. study has found no increase in Alzheimer's disease and other forms of dementia in 62,565 women who received chemotherapy for breast cancer. The women, who were at least 65 years old at diagnosis between 1991 and 2002, were initially free of cognitive impairments and were followed for up to 16 years. Perhaps surprisingly, the risk of developing Alzheimer disease, vascular dementia, or other dementias was found to be significantly lower in patients receiving chemotherapy for breast cancer. The risk of cognitive disorder was elevated, but not significantly different between the main study group and a control group. The authors concluded that this long-term study did not support the hypothesis that chemotherapy is associated with an increased risk of late stage cognitive impairments. In fact, the risk of developing Alzheimer disease, vascular dementia, or other dementias was significantly lower in patients receiving chemotherapy.

Other studies have also reported lower dementia risk for cancer patients

Those of us who have experienced "chemo brain" and have noted its similarities to early Alzheimer's will be relieved by the findings of this study. The cognitive impairment caused by chemotherapy in many breast cancer patients, which is well documented, can last for several years or even longer after treatment. However, according to this study, this cognitive impairment does not progress to Alzheimer's disease or other forms of outright dementia. The study was prospective, exceptionally large and had a relatively long follow-up period, all of which enhances its validity. On the other hand, little stratification was undertaken. It may be that unknown factors either increase or reduce the risk of late stage dementia for specific subgroups of women.

The study does not address possible reasons for the finding that dementia is actually less likely for women who undergo chemotherapy for breast cancer. However, this is not an isolated finding; previous studies have also found an inverse relationship between dementia and cancer (regardless of whether patients received chemotherapy). In fact, people with certain other disorders having a neurological component, such as Parkinson's disease, multiple sclerosis, and Down syndrome, have also been reported to get cancer less often than expected.