Esophageal cancer genetics in South Africa

Abstract

Esophageal cancer (EC) is an extremely aggressive cancer with one of the highest mortality rates. The cancer is generally only diagnosed at the later stages and has a poor 5-year survival rate due to the limited treatment options. China and South Africa are two countries with a very high prevalence rate of EC. EC rates in South Africa have been on the increase, and esophageal squamous cell carcinoma is the predominant subtype and a primary cause of cancer-related deaths in the black and male mixed ancestry populations in South Africa. The incidence of EC is highest in the Eastern Cape Province, especially in the rural areas such as the Transkei, where the consumption of foods contaminated with Fusarium verticillioides is thought to play a major contributing role to the incidence of EC. China is responsible for almost half of all new cases of EC globally. In China, the prevalence of EC varies greatly. However, the two main areas of high prevalence are the southern Taihang Mountain area (Linxian, Henan Province) and the north Jiangsu area. In both countries, environmental toxins play a major role in increasing the chance that an individual will develop EC. These associative factors include tobacco use, alcohol consumption, nutritional deficiencies and exposure to environmental toxins. However, genetic polymorphisms also play a role in predisposing individuals to EC. These include single-nucleotide polymorphisms that can be found in both protein-coding genes and in non-coding sequences such as miRNAs. The aim of this review is to summarize the contribution of genetic polymorphisms to EC in South Africa and to compare and contrast this to the genetic polymorphisms observed in EC in the most comprehensively studied population group, the Chinese.

Keywords: China; ESCC; South Africa; adenocarcinoma; alcohol; diet; esophageal squamous cell carcinoma; smoking.

Figure 1

Incidence and mortality rates of EC. Notes: (A) Worldwide in both sexes and (B) in men and women in Africa. The highest incidence rate is in South Africa and East Africa, with the highest incidence in both sexes being found in Kenya, Uganda and Malawi. A high incidence rate of EC is found in both sexes in Guinea Bissau. (C) The incidence and mortality rates per 100,000 in South Africa and the Eastern Africa and Southern Africa regions is much higher in males than in females. Abbreviation: EC, esophageal cancer.

Figure 2

Geographic locations of the four high-risk areas in China. Notes: The counties Cixian, Shexian and Linxian are located on the borders of the Henan and Hebei provinces. These three counties are located in an area with a radius of 60 km. The Taihang Mountains straddle the border of the Shanxi and Hebei provinces and have some of the highest mortality rates of esophageal cancer in the world. Another high-risk area for esophageal cancer is Yanting in Sichuan Province. Data from Lin et al.