Cancer survival tends to be far lower when patients have comorbid diseases, based on a systematic review of 10 years of data from Denmark and elsewhere. The effects of comorbidities on survival varied by cancer type, but overall trends were comparable, researchers said.

For example, 1-year survival for patients with bowel cancer alone was 80%, compared with 46% for patients who also had other diseases. In the case of breast cancer, 5-year survival was 83% without comorbid conditions, 64% for patients with one or two other chronic diseases, and 50% for patients with three or more diseases.

Chronic comorbid diseases such as diabetes, chronic obstructive pulmonary disease, arthritis, depression, and cardiovascular disease are a pervasive and expanding global problem. Poorer survival is expected when patients with cancer have comorbidities, said coauthor Henrik Toft Sørensen, MD, professor of clinical epidemiology at Aarhus University and Aarhus University Hospital, both in Denmark. But he added that the disparity in survival for these cancer patients persists.

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“These patients have not experienced the same progress in survival rates as other cancer patients have experienced during the last 15 years,” said Sørensen. “It has long been the case that cancer doctors are concerned with cancer, arthritis doctors with arthritis, and so on. But increasing attention is being paid to the significance of patients having other diseases.”

The systematic review included studies of comorbidity and breast, lung, and colon cancer performed in Denmark and elsewhere from 2002 to 2012. The results indicated that in Denmark, 40% of patients with cancer had been hospitalized for one or more other diseases. An estimated 30% of cancer patients had one or two comorbid diseases, and 10% had three or more. The study was published online by Clinical Epidemiology (2013; doi:10.2147/CLEP.S47150).

The analysis did not reveal all causes of mortality, said Mette Søgaard, PhD, of the department of clinical epidemiology at Aarhus University and Aarhus University Hospital.

“It is not clear what the patients die of—whether it is the cancer or the other diseases,” she said. “However, we can see that it is not due to the fact that they have a more aggressive cancer, that the disease is more advanced when detected, or that the patients are older.”

The analysis also showed that cancer patients with comorbidities did not receive the same treatment as other patients with cancer—perhaps because of decreased tolerance for cancer therapies. Patients with cancer and comorbid diseases have a markedly increased risk of complications, but are also more likely to receive either excessive or insufficient treatment, said Sørensen. Søgaard added, “There are still a lot of unanswered questions—not least [is] whether some of these patients are receiving too little treatment.”