Digestive tract cancers

Digestive tract cancers

http://survcan.iarc.fr/survivalchap32.php

Five-year survival prospects of patients with liver, pancreas, gallbladder, oesophagus and stomach cancers were generally poor, not exceeding 15% in most populations studied, indicating the poor prognosis of cancers in these organs and the importance of primary prevention in controlling these tumours. Most of the cancers arising in these sites are rarely curable. The overall 5-year survival rate in patients amenable for radical definitive treatment by surgery or radiotherapy for oesophageal cancer ranges from 5% to 30%. Cytological and endoscopic screening have been evaluated in countries with a high incidence of oesophageal cancer. Although these efforts have shown that it is possible to detect cancers in an early asymptomatic stage, and those with very early disease have a better chance of survival, screening is unlikely to reduce mortality from oesophageal cancer and may result in some serious side-effects associated with endoscopy such as aspiration, perforation, bleeding and cardiopulmonary events. Improving general nutrition and controlling tobacco and alcohol consumption are important in the context of preventing oesophageal cancer. Symptomatic gastroesophageal reflux disease (GERD) has been identified as a risk factor of oesophageal adenocarcinoma.

The survival outcome of patients with stomach cancer is related to tumour extension beyond the gastric wall, regional lymph node involvement, and to a lesser extent on tumour grade^{[14] [15]}. Screening is unlikely to reduce mortality from stomach cancer. Overall stomach cancer incidence and mortality are declining across the world due to better food preservation using refrigerators, reducied consumption of salted, smoked and pickled food products, and wide availability of fruits and vegetables the year round. Risk factors for gastric cancer include the presence of precursor conditions such as chronic atrophic gastritis, intestinal metaplasia and pernicious anaemia. There is increasing evidence that Helicobacter pylori infection of the stomach is associated with both the initiation and promotion of gastric carcinoma.

Most patients with stomach cancer present with metastatic disease, either regional or in distant sites such as the liver. The curative treatment option for stomach cancer is radical surgery; however, the frequency of local failure in the tumour bed and regional lymph nodes and distant failures via haematogenous or peritoneal routes remains high. Although 30–50% of patients with localized distal stomach cancer can be cured, such disease accounts for less than 10% of cases. On the other hand, the 5-year survival rate of patients with localized proximal stomach cancer is less than 15%. None with disseminated disease survive at 5 years.

Survival for colorectal (large bowel) cancer varied from 4% in the Gambia to % in Seoul, Republic of Korea. The survival figures were less than 8% in the sub-Saharan African countries of The Gambia and Uganda and less than 30% in Harare, Zimbabwe, all of which have poorly-developed cancer health care infrastructure and limited availability of and accessibility to curative treatments for most patients. The survival prospects of patients with large bowel cancer is clearly related to the degree of penetration of the tumour through the intestinal wall, the presence or absence of regional lymph nodal involvement, and the presence or absence of distant metastases; these three characteristics form the basis for staging and treatment options for this cancer^[16].

It is well established that screening with faecal occult blood testing reduces colorectal cancer mortality, and felexible sigmoidoscopy and colonoscopy leads to earlier detection of polyps and colorectal cancer. The standard treatment for patients with colon cancer has been open surgical resection of the primary and regional lymph nodes for localized disease. Patients with advanced disease may require combined modality therapy with chemotherapy with or without radiation therapy. The survival outcomes for colorectal cancer depend on the clinical stage at presentation and the ability of the health services to provide prompt standard care with radical surgery and other adjuvant therapies as indicated. Survival rates exceeding 50% reported from Hong Kong, the Republic of Korea, Singapore, regions in Thailand and mainland China seem to reflect the wide availability of screening, endoscopy and treatment in their well- or moderately-developed health services. The flexible sigmoidoscope permits a more complete examination of the distal colon with more acceptable patient tolerance than the rigid sigmoidoscope. Virtually all the screening studies using these types of sigmoidoscopes have demonstrated an increase in the proportion of early cases and survival compared with cases diagnosed in a routine environment. It is quite likely that the early recognition of the clinical importance of flat lesions detected in colonoscopy by the endoscopy practices in east Asian countries has also led to earlier detection of colorectal cancers there^[17]. The survival experience of large bowel cancer patients in Hong Kong and Republic of Korea are similar to that reported for white patients in the United States Surveillance Epidemiology and End Results (US-SEER)^[9].

The survival rates of localized and regional large bowel cancer were 64% and 46% respectively in Singapore and Izmir Turkey, as compared to 50% and 32% respectively in countries with less-developed health services such as Thailand, India and the Philippines (Figure 4a). It is interesting to note that the survival experience of localized colorectal cancer patients in countries with less-developed health services and that of patients with regional disease in countries such as Singapore and Turkey with well-developed health services were almost similar. The higher survival in Singapore and Turkey seems to be a reflection of both earlier stages of clinical presentation and the capability of the health services to promptly respond with early diagnosis and comprehensive management. On the other hand, the wide difference in the outcome between localized and regional cancers (18 percentage points) indicates the potential for early detection to prevent more deaths from colorectal cancer.

The vast majority of patients with liver cancer die within a year, although a small fraction of those with localized cancers can be potentially cured by surgical resection. However, screening for liver cancer with ultrasonography and/or alpha fetoprotein (AFP) estimation does not reduce liver cancer mortality^{[18] [19]}. A vast majority of liver cancers are caused by chronic infection with Hepatitis B (HBV) or C (HCV) viruses, ingestion of foods contaminated with aflatoxin and alcohol consumption. Controlling these risk factors has a major impact on liver cancer prevention. A 69% reduction in the incidence of liver cancer among the vaccinated cohort has been recently demonstrated after the introduction of HBV vaccination in the national immunization programme of Taiwan^[20].

Cancer of the pancreas is rarely curable, although complete surgical excision in patients with localized disease and small cancers (<2 cm) with no lymph node metastases and no extension beyond the capsule of the pancreas can result in 5-year survival rates around 20%. It is quite likely that survival rates exceeding 15–20% for these poor-prognosis cancers in our series suffer from over-estimation due to under-ascertainment of death events in many patients who might have been misclassified as alive at the closing date.

Conclusion

In summary, our results imply that the levels of development of health services and their efficiency in providing early diagnosis, treatment and clinical follow-up care have a profound impact on survival from cancer. Survival outcomes were higher in countries with highly-developed health services than in countries with less-developed services.

The critical concentration of trained human resources for cancer control is definitely higher in developed health care services. The large variation in survival observed within populations in different regions of China, India and Thailand reflects the varying levels of development of cancer health services and the availability of trained personnel within these countries, particularly in urban vs. rural areas. All three regions in the Republic of Korea showed no major differences in survival for any cancer, possibly reflecting equitably developed and accessible health care services across the country. The poor survival rates observed in The Gambia, Uganda and Zimbabwe emphasize the importance and urgent need for direct vertical investments to improve health services and to generate sufficient trained human resources by national governments of sub-Saharan African and other developing countries. It is quite likely that the survival rates in many low- and medium-resourced countries that were not included in this study, particularly those from sub-Saharan Africa, would be lower than those reported in our study.

This study would not have been possible without the availability of reliable population-based cancer registries. It is important to organize such information systems in the regions/countries that lack them. However, the registries must collect more reliable information on clinical stages, particularly in terms of composite clinical stages and Tumour, Node, Metastasis (TNM) categories according to internationally-accepted stage classifications and summary treatment data to explain the observed survival patterns and differences between different populations in a convincing manner. The staging information in terms of composite stages and/or TNM categories should be collected at least for treatable forms of cancers such as oral cavity, larynx, breast, cervix, ovary, lymphomas and childhood cancers. Treatment information in terms of proportions of patients completing prescribed treatment will be an important measure of health service efficiency and will be useful to describe observed survival variations.

Striking differences in cancer survival between countries reflect the large inequality in accessible and available cancer health services for populations across the world, and such inequality is clearly unacceptable. Health services needs to be upgraded for cancers where there exist marked differences in survival for localized cancer between well-developed and less-developed countries. Urgent and adequate investment by countries in comprehensive cancer control, including improving public and professional awareness, early detection, prompt treatment using locally feasible yet effective regimens, health services infrastructure, human resources development and referral pathways, will reduce such inequality and ensure improved and equitable accessibility to health services. The current data can serve as a baseline to evaluate improvements in cancer control and cancer health services in the future.