Cancer incidence in indigenous populations of Western Amazon, Brazil

This study aims to estimate a population-based cancer incidence among indigenous populations in the State of Acre, Brazilian Western Amazon, to provide knowledge about cancer epidemiological profiles contributing to healthcare policies and service planning. Although cancer epidemiology in Brazil is well described through incidence and mortality estimate in the general population, cancer estimates among indigenous peoples are still unknown.

This is a descriptive study of cancer incidence among the indigenous population (2000-2012) in the State of Acre, Brazil. The sources used were population-based cancer registries of Goiânia, hospital-based cancer registry of Acre, São Paulo, and Porto Velho; Special Indigenous Health Districts databases of Acre, Goiânia, and São Paulo; Mortality Information System, and Rio Branco's public and private laboratories' reports. Standardized Incidence Ratio (SIR) was calculated using cancer incidence rates of Goiânia as reference.

From 137 cancer cases, 51.8% occurred in women and 32.1% in people aged 70 + . Among men, the most frequent cancer sites were stomach (25.8%), liver (15.1%), colorectal (7.6%), leukemia (7.6%), and prostate (6.1%). Among women, the most frequent were cervical (50.7%), stomach (8.5%), leukemia (5.6%), liver (4.3%), and breast (4.3%). Among men, there was an excess of cancer cases for stomach (SIR=1.75; 95%CI:1.67-1.83), liver (SIR=1.77; 95%CI:1.66-1.88), and leukemia (SIR=1.64; 95%CI:1.49-1.78). In women, an excess of cancer cases was observed for cervical (SIR=4.49; 95%CI:4.34-4.64) and liver (SIR=2.11; 95%CI:1.88-2.34). A lower cancer incidence for prostate (SIR=0.06; 95%CI:0.05-0.07) and female breast (SIR=0.12; 95%CI:0.11-0.14) was observed.

Cervical, stomach, and liver cancers corresponded to 52% of the cases and were highly incident among the Brazilian indigenous population of Western Amazon compared to non-indigenous counterparts. Despite the low frequency of breast and prostate cancer, the fact they were present among indigenous peoples suggests a complex epidemiological transition framework in these populations.