Obesity could increase the risk of many chronic diseases, including hypertension, cardiovascular diseases, high lipid level, diabetes, stroke, endometrial cancer and certain types of cancer which could benefit by secondary prevention through screening programs. In particular, colorectal, breast and prostate cancer (these three cancers will be named as "obesity-related cancers" thereafter) demonstrate a rapidly increasing trend of incidence in Asia in the past decade. The World Cancer Research Fund of the American Institute for Cancer Research has reviewed all the studies about the link between obesity and cancer . For colorectal cancer (CRC), there is compelling evidence suggesting that obesity is associated with 30-66% higher risk of developing CRC. Weight gain during adulthood was also shown to increase risk of CRC. As for breast cancer, post-menopausal women with the smallest waist (compared with the largest) had 39% lower risk of getting breast cancer . A 5-unit increase in BMI is associated with 12% increased risk of breast cancer, and this figure escalates to 20-40% for postmenopausal women. For prostate cancer, greater body fatness has been suggested as a reason of advanced prostate cancer. Obesity was positively related to advanced stage prostate cancer. The relative risk is 1.09 for every 5 kg/m2 higher BMI.

Among Chinese adults of Hong Kong in 2014, 39% were overweight or obese (compared with 20.9% reported in European adults in the same year) and up to 69.7% reported that they did not perform any measures to achieve optimal weight control. Men (49.6%) had a higher proportion of overweight or obesity than females (29.5%). Adults who are aged 45-54 had the highest rate (50.5%) of overweight or obesity than other age groups. In addition, there were 62.5% whose physical activity level did not meet the recommendations from the World Health Organization (WHO). Only 18.7% consumed at least 5 portions of fruit and vegetables per day; yet about 30% were alcoholic drinkers; and more than 10% were daily or occasional smoker. These figures imply that the incidence of obesity and obesity-related cancers will further escalate - and urgent actions at the community level are needed to combat the rising incidence and mortality of these conditions.

As shown in Figure 2, the discrepancy between the number of new cases (incidence) and number of deaths (mortality) is much higher for colorectal, breast and prostate cancer as compared to other cancers. It is well recognized that screening could effectively reduce mortality for these three obesity-related cancers when they are detected at an earlier stage.

Primary prevention is one of the crucial strategies found to be effective in cancer prevention. Health education on modification of lifestyle factors is especially useful to change behavior and reduce the impact of the threats posed by obesity and its related cancers. The application of behavioral medicine, defined as "the interdisciplinary field concerned with the development and integration of sociocultural, psychosocial, behavioral, and biomedical knowledge relevant to health and illness and the application of this knowledge to disease prevention, health promotion, etiology, diagnosis, treatment, and rehabilitation'', has been considered to be the most effective and practical means to prevent cancers. A comprehensive strategy for reducing cancers also includes secondary prevention that aims at early detection of diseases. Early detection for some "screen-relevant" cancers is particularly effective to reduce cancer-related mortality.

The concept of a one-stop approach to screen for multiple cancers is relatively novel from existing literature - and one of such initiatives is the "Integrated Cancer Prevention Centre" (ICPC) established in Tel Aviv Sourasky Medical Center at Israel in 2006. Analysis of the first 1,000 subjects visiting the centre showed that the compliance at the centre was higher than those seen in the Ministry of Health for the general population (78% vs. 60% for mammography; 39% vs. 16% for colonoscopy). The provision of such a unique facility designed for one-stop screening for multiple cancers was found to be feasible, with an ability to detect a wide range of neoplastic lesions at an early stage. In the recent decade, there are also emerging centres that have been established as multi-cancer screening clinics worldwide. Nevertheless, there is a scarcity of studies that have highlighted the outcomes of these multi-cancer screening programs.