A pre-existing diagnosis of dementia was associated with increased risk of death for older patients with advanced colon cancer; however, some of the effects of dementia on survival could be mediated by receipt of chemotherapy.

The recent study was published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.

Yingjia Chen, PhD, a postdoctoral fellow in the Memory and Aging Center in the Department of Neurology at University of California, San Francisco, started by performing a retrospective cohort study using SEER-Medicare data for 3,903 adults over the age of 65 with confirmed diagnoses of stage 3 colon cancer and dementia.

Of them, 60.9 percent were women, and 79.7 percent were white.

A pre-existing dementia diagnosis was confirmed by a formal entry in medical records or prescription records for one of four FDA-approved drugs for temporarily improving dementia symptoms: donepezil, galantamine, memantine, and rivastigmine.

The researchers found that a pre-existing diagnosis of dementia was associated with increased risk of death by 45 percent and the average mean survival time for patients with stage 3 colon cancer and pre-existing dementia was only 57 percent that of their cognitively healthy counterparts.

Next, Chen and colleagues examined the impact of the receipt of chemotherapy on survival outcome in patients with dementia.

"We assessed the mediating effect of chemotherapy using a statistical method called accelerated failure time model in the context of the counterfactual framework and found that the receipt of chemotherapy was significantly associated with survival," explained Chen. "This type of analysis allowed us to determine that not receiving chemotherapy accounted for 13 percent of the poorer survival outcomes for patients with pre-existing dementia.

"Both colon cancer and dementia are prevalent among the growing elderly population and have a high risk of co-occurrence," said Chen. "Chemotherapy may be challenging for older adults with dementia, but our research shows that some may still benefit."

"In general, dementia patients with advanced colon cancer are being undertreated. There are many good reasons why physicians, patients, and families may decide to forgo chemotherapy, including toxicity, functional limitations of the patient, or if patients are diagnosed with colon cancer at later stages," Chen explained. "However, our findings suggest that chemotherapy may increase survival and should be considered for advanced colon cancer patients with dementia in a similar fashion as for those without dementia."

Limitations of the study include that detailed information about dementia diagnoses or functional status were not available, so the researchers were not able to identify the extent of dementia

The investigators were also unable to know the reasons why chemotherapy was or was not chosen, nor the regimens administered.

Source: American Association for Cancer Research