Results
We report the results of the three analyses on (1) relationships between cancers and non-cancer diseases; (2) relationships between cancers and diseases from two classes—nervous system diseases and metabolic diseases; and (3) colorectal cancer comorbidities. In each analysis, we show how the comorbidity patterns change with age and gender.
Cancer comorbidity patterns change with age and gender. We first combined all cancers regardless of their types and stages, and ranked non-cancer diseases by their relevance scores (obtained from random walk) within each age group. A higher relevance score indicates a stronger comorbidity association with cancers.
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We found that cancers are associated with a broad spectrum of diseases, and cancer comorbidity patterns change with age.
Across the five age groups (,20, 20–40, 40–60, 60–80, and .80 years), we extracted 73 cancer comorbidities, and categorized them into 12 different disease classes. Table 1 lists the 12 disease classes, which are sorted by the variations of their average relevance scores across different age groups. Cardiovascular diseases have greatly varying scores, which indicate that age largely affects the comorbidity relationships between cancers and cardiovascular diseases.
On the contrary, liver diseases have the most stable score among the 12 disease classes, which indicate that their comorbidity relationships with cancers are relatively independent of patient ages. We also compared the relevance scores and the prevalence of the 12 disease classes among different age groups. Table 1 shows that the scores of cardiovascular diseases are highly correlated with their prevalence.
Since the high prevalence of a disease increases the probability of co-occurring with other diseases among the population, the comorbidity relationship between cardiovascular diseases and cancers might be overestimated.
Table 1. Score variations for 12 disease classes, which cover 73 cancer comorbidities, across all patient groups stratified by age.
| DISEASE CLASSES | SCORE VARIATION | SCORE-PREVALENCE CORRELATION |
| Cardiovascular diseases* | 0.060 | 0.974 |
| Communicable diseases | 0.060 | –0.425 |
| Immune system diseases | 0.037 | 0.112 |
| Kidney diseases | 0.037 | 0.873 |
| Respiration disorders* | 0.035 | –0.465 |
| Dermatitis | 0.034 | 0.789 |
| Digestive system diseases* | 0.025 | –0.676 |
| Nervous system diseases* | 0.021 | 0.239 |
| Inflammatory disorders | 0.018 | 0.797 |
| Endocrine, nutritional and metabolic diseases* | 0.014 | 0.228 |
| Autoimmune diseases* | 0.013 | –0.161 |
| Liver diseases | 0.013 | –0.361 |
| Notes: *Disease classes with non-zero relevance scores in all age groups. | ||
Figure 3 shows the variation trends of cancer comorbidity patterns for six disease classes, which have non-zero relevance scores in all age groups (the disease classes with asterisks in Table 1).
Cardiovascular diseases have a stronger association with cancers when patients become elder and the association peaks in the age group 60–80. Respiration disorders occur more frequently among younger cancer patients, particularly in the age group <20. The other disease classes have relatively stable comorbidity associations with cancer when patient ages increase.
(Click on above figure to enlarge.)
We repeated the analysis between cancers and non-cancer diseases among the two gender groups. The results show that gender has little impact on most disease classes except for cardiovascular diseases, which are more common among male cancer patients, and digestive system diseases, which have a stronger association with cancers among female (Fig. 4).
(Click on above figure to enlarge.)
