In older people, who generally have more chronic illnesses than the young, cancer is often diagnosed later and mortality rates are higher. Some studies have blamed that effect on other health conditions that may mask the early symptoms of cancer, or the chronic disease may demand more immediate attention of primary care physicians, who then fail to screen for cancer. On the other hand, since people with comorbidities see clinicians more frequently, there are more opportunities for preventive care, including cancer screening.
Though studies have clearly linked comorbidities with later stage diagnoses of a variety of cancers, some results are less straightforward. Researchers reported in 2005 that specific comorbid conditions directly impacted whether a woman was diagnosed with breast cancer earlier or later in life. Cardiovascular disease, musculoskeletal disorders, most gastrointestinal disease and noninvasive breast disease contributed to earlier breast cancer detection, while diabetes, other endocrine disorders, psychiatric disorders and hematologic disorders did the opposite. Overall, investigators found that mammography screening and contact with the medical care system decreased the probability of late-stage diagnosis.
For regularly screened cancers, such as breast and colon, researchers see a positive effect of comorbidities, especially those that demand regular visits to healthcare providers. The effect is less clear in other cancers, such as lung, ovarian or brain, for which screening is less common. Because comorbidities are quite common—one study estimated nearly 70 percent of cancer patients have other chronic illnesses—many clinicians call for more research in the area of early detection.