Table 1 shows the mean incidence (per 100,000 population) of 13 cancers in 487 CRIs. This highlights the variation in incidence. The mean incidence varied strongly between cancers, with the top three being lung, liver, and stomach cancers (56.0, 29.1, and 29.0) and the bottom three being kidney, gallbladder, and bone cancers (4.1, 3.6, and 2.0). There were also large spatial differences within the same cancer type, e.g., the highest incidence of lung cancer was 16 times higher than the lowest incidence (151.76 vs. 9.51), and the highest incidence of bone cancer was 28 times higher than the lowest incidence (6.23 vs 0.22) across all CRIs.
Spatial clustering of single cancer type
From a spatial perspective, global Moran’s I showed that there was spatial clustering of incidence for all the cancer types (P < 0.05, Table S1, Additional file 1). Dramatic spatial variation could be observed within each cancer (Fig. 1). Figure 2 shows the mean incidence and the incidence rate ratio (RR) of the five spatial patterns (i.e., HH, HL, NS, LH, LL), which differed significantly within each cancer. For all cancers analyzed, the RR showed a similar dose–response relationship with spatial clustering patterns, i.e., RR decreased from H to M and L groups. The largest variation of RRs was in esophageal cancer, where the highest value was 6.79 times the lowest. The smallest variation was in lung cancer, where the highest was 2.07 times the lowest (Fig. 2). Some correlations between cancer pairs were universal, such as the Pearson coefficients of 0.45 between lung and breast cancers and 0.47 between lung and kidney cancers (Figure S3, Additional file1). There was also some degree of overlap in terms of spatial distribution among the cancer types.
Figure 1 shows the spatial clustering patterns of all the analyzed cancers, showing both large variations and a degree of similarity. Figure 1a shows that the distribution of spatial clustering patterns of lung cancer was very similar to breast cancer. The HH clusters were mainly distributed in coastal and northern provinces, and 65.8% of lung cancer HH clusters overlapped with 62.9% of breast cancer HH clusters. Figure 1b shows the distribution of spatial clustering patterns of digestive system cancers. The most obvious feature is that the HH clusters of esophageal, stomach, and gallbladder cancers were mainly distributed in the east–west belt. There was a strong correlation between esophageal and stomach cancer (Pearson coefficient 0.58, Figure S3, Additional file 1), with 65.4% and 62.6% of HH clusters overlapping each other. Overall, 49.6% and 64.5% of HH clusters overlapped for stomach and gallbladder cancers (Pearson coefficient of 0.21).
Figure 1c shows the spatial clustering patterns of the five relatively uncommon cancers. In addition to the very similar clustering pattern with pancreatic cancer, kidney cancer was also very similar to breast cancer and lung cancer, and the Pearson coefficients ranged from 0.42 to 0.65 between the four cancers. The highest overlap was between breast cancer and kidney cancer, with 80.45% of kidney cancer HH clusters overlapping with 59.3% of breast cancer HH clusters.
For two hematological cancers, lymphoma and leukemia, the HH clusters were mainly located in the southeast (98.3% and 89.5%) and they were strongly correlated (Pearson correlation of 0.60). For brain and bone cancer, NS clusters predominated, indicating a relatively sporadic state, especially for bone cancer (accounting for 66.1% of the CRIs). It was not strongly correlated with any other cancers.
Spatial co-occurrence of multiple cancer types
Figure 3a shows the distribution of high-, medium-, and low-risk areas for the co-occurrence of multiple cancers. Overall, 83 areas (17.1%) were high-risk, 254 (52.2%) medium-risk, and 149 (30.7%) low-risk. High-risk areas were mainly located in the east coastal (Shandong, Shanghai, Jiangsu, and Zhejiang) and northeast (Jilin and Liaoning) areas. Low-risk areas were mainly located in the south, and medium-risk areas were scattered throughout mainland China. The mean total cancer incidence was 282, 208, and 175 per 100,000 population in each type of area, and the RRs (95% CI) of high- and medium-risk areas compared with low-risk areas were 1.61 (1.53–1.69) and 1.19 (1.14–1.23), with no overlap in the 95% CI (Fig. 3a).
The plausibility of the definition was further validated by kvthe observed monotonically increasing or decreasing trend of cancer incidence within high-risk and low-risk areas. The mean incidence of total cancer increased by 22 cases per 100,000 population for each increase in the number of cancers in the H group (i.e. when six, seven, eight, and more than eight of 13 cancers were identified as H group) in high-risk areas regardless of whether the cancer was common or uncommon. In low-risk areas, the mean incidence of total cancer decreased by 11 cases per 100,000 population for each increase in the number of cancers in the L group (P < 0.05, Figure S4, Additional file 1). This suggests that the spatial co-occurrence of cancers has a cumulative effect.
The proportion of the CRIs in different risk-type areas of spatial co-occurrence for multiple cancers in each province is shown in Fig. 3b. Except in the provinces with fewer CRIs (Shanghai, Beijing, Tibet, etc.), the CRIs in most provinces did not occur in only one kind of risk area. Zhejiang had the highest proportion of high-risk areas (85.7%), and Hunan the highest proportion of low-risk areas (86.4%).
Table S2a–S2c(Additional file 1) shows the proportions of CRIs in each of the three hierarchical incidence groups (H, M, and L groups) for each cancer type in each province. As the proportion increases, there is more likelihood that cancers co-occurred in the same CRI. We therefore selected cancers with proportions ≥ 50% to visualize the co-occurrence pattern. Figure 4a–c shows the detailed cancer co-occurrence pattern for each province across different risk areas.
In general, the co-occurrence of cancers was ubiquitous regardless of risk-type areas but the types of cancer involved varied greatly. In the high-risk areas (Fig. 4a), 10 types of cancers co-occurred in Shanghai and Zhejiang, but only one pair of cancers co-occurred in Chongqing and Hubei (lung and lymphoma). In the high-risk areas, lung, breast, colorectal, pancreatic, and kidney cancers were the most frequently observed cancers in the northeast, and lung, breast, stomach, gallbladder, and pancreatic cancers in the eastern coastal region. In the 15 provinces with high-risk areas, lung and pancreatic cancers occurred most frequently together (in nine provinces), followed by breast, stomach, colorectal, gallbladder, and kidney cancers (in seven provinces). For the 30 provinces (except Shanghai) with medium-risk areas, the most frequently observed cancers were brain cancer, bone cancer, leukemia, and gallbladder cancer, which occurred in at least 16 provinces (Fig. 4b). In low-risk areas, the co-occurrence pattern containing lung, colorectal, and liver cancers and lymphoma was the most frequently observed in the 12 northern provinces. The co-occurrence pattern containing esophageal, stomach, gallbladder, pancreatic, and kidney cancer was the most frequently observed in the 12 southern provinces (Fig. 4c).
Table S3 (Additional file 1) shows the PAF of high- and medium-risk areas compared with low-risk areas for each province. The PAF ranged from 7.6–37.9% for high-risk areas and 1.8–15.9% for medium-risk areas. The ECs ranged from 329 (Chongqing) to 32,590 (Jiangsu) for high-risk areas and 18 (Tibet) to 5,442 (Chongqing). The highest total number of ECs was in Jiangsu and the lowest was in Tibet. The total across all CRIs was 44,568.
Table 1. Basic statistics of incidence rate per 100, 000 of analyzed cancers.
Cancer site
|
ICD-10
|
N
|
Mean
|
Std
|
Minimum
|
p25
|
p50
|
p75
|
Maximum
|
Total
|
|
487
|
210·69
|
53·53
|
55·13
|
170·53
|
199·23
|
242·55
|
450·98
|
Lung
|
C33-34
|
487
|
55·99
|
18·86
|
9·51
|
43·50
|
52·09
|
67·71
|
151·76
|
Liver
|
C22
|
487
|
29·10
|
11·84
|
5·16
|
21·90
|
27·22
|
32·99
|
122·02
|
Stomach
|
C16
|
487
|
28·97
|
18·92
|
3·58
|
15·92
|
24·55
|
36·13
|
131·37
|
Colorectal
|
C18-21
|
487
|
25·67
|
10·47
|
1·90
|
18·05
|
23·46
|
32·06
|
74·11
|
Esophageal
|
C15
|
486
|
19·49
|
17·76
|
0·60
|
7·40
|
13·41
|
25·58
|
103·38
|
Breast
|
C50
|
487
|
17·81
|
7·97
|
1·38
|
12·36
|
16·26
|
22·73
|
46·88
|
Brain
|
C70-72, D32-33, D42-43
|
487
|
7·09
|
3·05
|
1·06
|
4·99
|
6·81
|
8·73
|
21·37
|
Pancreatic
|
C25
|
487
|
6·44
|
4·16
|
0·34
|
3·84
|
5·34
|
8·13
|
46·63
|
Leukemia
|
C81-86,88,90,96
|
470
|
5·54
|
2·55
|
0·22
|
3·90
|
5·36
|
7·15
|
19·93
|
Lymphoma
|
C91-95, D45-47
|
466
|
5·46
|
3·01
|
0·19
|
3·15
|
5·17
|
7·16
|
19·06
|
Kidney
|
C64-66,68
|
483
|
4·08
|
2·78
|
0·25
|
2·18
|
3·37
|
5·12
|
16·89
|
Gallbladder
|
C23-24
|
481
|
3·56
|
2·18
|
0·29
|
1·93
|
3·08
|
4·67
|
12·87
|
Bone
|
C40-41
|
485
|
2·02
|
1·03
|
0·22
|
1·27
|
1·86
|
2·53
|
6·23
|