| [Background]Colorectal cancer incidence growed fast these years and became the third most common cause of cancer in the world. Age-adjusted incidence rates rise to the third place among males and the second place among females during 2005 in urban Shanghai.Obesity was not only a disease itself, but also associated with the increased risk of many chronic diseases. Obesity was considered as the fifth risk factor that affect to human health. The World Cancer Research Fund (WCRF) Report in 2007 concluded that it was related to the risk of colorectal cancer was convincing. A number of cohorts found that obesity was positively associated with the risk of colorectal cancer. But the findings in these studies were inconsistent. Some factors might affect the result, such as abdominal obesity, subsite of colorectal, menopause status and HRT using. Most of these cohort studies were conducted in west countries with high prevelance both for colorectal cancer and obesity. Rarely cohort study was carried out in Asia which the prevelance in colorectal cancer and obesity was relatively low.Our study will firstly focus on the time trend analysis of colorectal cancer in urban Shanghai by means of the data from the Shanghai Cancer Registry, and then to investigate the relation between obese and risk of colon and rectum cancers in our on-going prospective women cohort study.[Objectives]1:To explore the time trends of colorectal cancer incidence in urban Shanghai from 1973 to 2005 by using data collected in Shanghai Cancer Registry.2:To investigate the association between obesity and colorectal cancer risk in a population-based cohort study-the Shanghai Women Health Study (SWHS).[Method]Data on the incidence rates of colorectal cancer were obtained from a population-based cancer registry in Shanghai. A total of 32,962 colon cancer and 24,662 rectal cancers were registered during 1973-2005. Population estimation was based on periodic censuses, with age-and sex-specific annual estimates derived for the remaining years. The incidence rates were adjusted to the world standard population by using the direct method. Annul percent changes (APCs) in rates were estimated by means of a linear regression of the logarithm of the respective rates on calendar, weighted by the number of incidence cases.A total of 74,942 female residents aged 40 to 70 years in urban Shanghai were recruited in a prospective cohort study (the Shanghai Women Health Study) during 1997 through 2000, and were actively followed up biennially. By the end of 2008,557 incident cases of colorectal cancer were identified in the cohort. Cox regression model was used to estimate the adjusted relative risks (RRs) and 95% confidence intervals (CIs). SAS software (version 8.2) was used in the data analysis.[Results]Between 1973 to 2005, the age-adjusted incidence rates of colon cancer increased from 6.09 per 100,000 and 5.70 per 100,000 to 14.70 per 100,000 and 14.35 per 100,000 in male and in female respectively. The APCs were 3.03%(t=14.77, P＜0.01) and 3.21%(t=22.15, P＜0.01). The rates of rectum cancer increased from 7.68 and 6.51 to 11.45 and 8.28 in male and in female respectively, with the APCs of 1.34%(t=7.28, P＜0.01) and 0.93%(t=7.34, P＜0.01). Age-specific rates were increased along with age (male colon cancer: t=13.17, P<0.01; male rectal cancer: t=12.30, P＜0.01; female colon cancer:t=9.46, P＜0.01; female rectal cancer:t=9.02, P<0.01), and reach to top at ages of 80-for colorectal cancer in both male and female (male colon cancer: 191.39/100,000; male rectal cancer:125.48/100,000; female colon cancer:156.34/100,000; female rectal cancer: 79.06/100,000;). The top APCs for colon and rectum cancer in female were 5.86% and 2.79% at age above 85 and in male those were 4.64% and 2.38% at age group of 80-. The APCs of colon cancer were greater than those of rectum cancer at the groups above 45 years old. The average ages when diagnosed were delayed from 57-60 to 66-70 during these 33 years. The average diagnosed ages of colon cancer were later than those of rectum cancer slightly (male colon cancer:68.61±12.17, male rectal cancer 66.81±12.62; female colon cancer:69.20±12.13, female rectal cancer:67.75±12.54)During an average 10.05 person-years of follow up, a total of 557 women were diagnosed with incident colorectal cancer (343 for colon cancer and 214 for rectum cancer). The prevalence of overweight (24≤BMI<28) and overall obesity (BMI≥28) were 34.58% and 12.18%, respectively. Compared with 18.5≤BMI＜24, the multivariate relative risk(RR) of colorectal cancer was 1.02 (95%CI,0.80-1.31, P-trend=0.43) for BMI≥28. The RRs for different abdominal obesity indexes (WC≥80, WHR≥0.85, WHtR≥0.5) were 0.92,0.96,0.92 and all p for trend were great than 0.05. There were no association between obesity related indexes and different cancer subsites. Menopause status and HRT using did not change the association between obesity and colorectal cancer risk. For a further stratified analysis, the obesity (BMI≥28) had an increased risk of colorectal cancer compared with the normal (18.5≤BMI<24) in those whose WHtR was less than 0.5. The RR was 3.18 (95%CI:1.02-9.96, P-trend=0.0234).The positive associations were especially for rectal cancer (RR=5.59), but not for colon cancer. Among participants whose BMI was less than 24, compared with the lowest quintile of WC, WHtR and WsHtR, RRs for the highest quintile were 2.09(95%CI:1.16-3.78),2.36(95%CI:1.33-4.18), 1.92(95%CI:1.12-3.28), respectively. These positive associations were only found in colon cancer, not in rectal cancer.[Conclusions]1. The incidence rates of colorectal cancer increased steadily in urban Shanghai during 1973 and 2005, especially for colon cancer.2. The average ages when diagnosed were delayed about 10 years during these 33 years. The average diagnosed ages of colon cancer were later than those of rectum cancer slightly.3. The prevalences of overweight and overall obesity were 34.58% and 12.18% respectively in middle-aged and elder women in urban Shanghai.4. There were no distinctive associations between obesity index and different colorectal cancer subsites. Menopause status and HRT using did not change the association between obesity and colorectal cancer.5. Indexes of abdominal obesity were shown to increase the risk of colon cancer in those BMI was in normal range. |
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