STUDY DESIGN AND SCOPE

This narrative review incorporates integrative elements to map and interprets potential links between environmental degradation, climate variability, and cancer in the Amazon. The approach privileges breadth and triangulation across epidemiology, exposure science, molecular mechanisms, health systems, and ethical-social analyses. The synthesis is qualitative; no meta-analysis was conducted.

CONCEPTUAL FRAMEWORK

Selection, appraisal, and synthesis were guided by the Planetary Health and Environmental Justice frameworks. Evidence was organized along exposure-pathway-outcome axes relevant to the Amazon: inhaled toxicants from biomass burning, solar ultraviolet (UV) exposure, heavy metals and other contaminants in water and food webs, and climate-related disruptions to oncological care.

INFORMATION SOURCES AND SEARCH STRATEGY

We searched PubMed/MEDLINE, Scopus, Web of Science, SciELO, and LILACS, complemented by targeted Google Scholar queries and backward/forward citation tracking from key papers already known to the authors. The search prioritized studies published mostly from March 2014 to March 2025, encompassing the most recent decade of research. Search strings combined controlled vocabulary and free text in English, Portuguese, and Spanish, including terms such as Amazon/Amazônia/Amazonas, climate change, wildfire smoke, PM _2.5 , PAH, mercury/methylmercury, artisanal gold mining, ultraviolet radiation, cancer, Indigenous health, environmental justice, health-system resilience, cancer incidence/mortality, biomarkers, and exposure assessment.

ELIGIBILITY CRITERIA

Inclusion: peer-reviewed studies and authoritative reports addressing Amazonian populations or ecosystems and at least one of the following: carcinogenic exposures pertinent to the region; cancer outcomes (incidence, mortality, staging, survival); mechanistic endpoints plausibly linked to carcinogenesis with contextual applicability; or health-system impacts of climate extremes relevant to cancer care. Eligible study designs included cohort, case-control, time-series, and cross-sectional epidemiological studies, as well as environmental exposure assessments, experimental/mechanistic investigations, and health-systems or implementation research.

Exclusion: studies outside the Amazon without transferable mechanisms; purely ecological papers lacking a health or exposure link; non-peer-reviewed opinion pieces; and animal or in vitro studies with limited generalizability to Amazonian conditions.

SCREENING, DATA EXTRACTION, AND SYNTHESIS

Titles and abstracts were screened for relevance, and full texts were reviewed when appropriate. Reference lists of included studies were also examined to identify additional region-specific evidence. The studies were analyzed with attention to their design, context, population, exposures, outcomes, and limitations. Their main contributions were integrated thematically across four domains: air pollution and wildfires; UV radiation and cancer; heavy metals and food-web contamination; and climate extremes affecting cancer care and equity.

AIR POLLUTION AND FOREST FIRES: INHALED CARCINOGENS AND THEIR ONCOLOGICAL IMPACT

Forest fires in the Amazon, exacerbated by climate change and human activities such as deforestation, are a major source of atmospheric pollution. The smoke produced by these fires is a complex mixture of substances that includes known human carcinogens such as particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), and various volatile organic compounds (VOCs)². Smoke from fires in the Amazon can be extremely toxic, reflecting the severity of air-quality degradation¹⁰. Researchers have confirmed that wildfire smoke can induce cancer, with studies demonstrating how this smoke causes genetic damage and leads to human lung-cell death, revealing a direct biological mechanism for carcinogenesis¹¹.

Exposure to pollutants from wildfires has been linked to an increased risk of respiratory cancers, including lung cancer, and there is some evidence suggesting associations with other malignancies such as brain tumors. A long-term study conducted by McGill University observed that individuals residing within a 50 km radius of wildfires had a higher incidence of brain tumors (10%) and lung cancer (4.9%), indicating a potential correlation between proximity to wildfires and cancer risk. Chronic exposure is a concern, as wildfires recur annually in some areas, potentially leading to repeated exposure to carcinogenic pollutants. Research on wildland firefighters also suggests they may have an increased risk of lung cancer, with estimates ranging from 8% to 43%. While these findings raise important public-health considerations, more research is needed to establish definitive causal relationships between wildfire exposure and cancer¹². Furthermore, exposure to wildfires has been associated with poorer survival outcomes in patients recovering from lung-cancer surgery, underscoring the increased vulnerability of individuals with preexisting conditions¹³. Researchers emphasize that wildfires often recur in the same regions each year, meaning that nearby communities may face ongoing exposure to PMs^14)-(17.

The annual recurrence of forest fires results in chronic exposure to a persistent burden of carcinogens for nearby populations, with health risks extending far beyond the active burning period. After the fires are extinguished, pollutants such as heavy metals and PAHs remain in the environment, contaminating air, soil, and water through deposition and runoff, and persisting for extended periods¹⁸. Chronic exposure to these substances causes cumulative DNA damage and impairs cellular repair mechanisms, which are critical drivers of cancer development¹⁹. Studies have shown that the health risks associated with such chronic, low-level exposure are often underestimated compared with those of acute events. Nonetheless, they contribute to long-term increases in respiratory and other cancers, as well as cardiovascular disease¹².

The toxicity of wildfire smoke is not merely the sum of its pollutants; rather, the complex mixture - including PM_2.5, PAHs, VOCs, and heavy metals - can interact synergistically, amplifying overall toxic and carcinogenic effects^20),(21. This complexity makes it difficult to isolate single causative agents, necessitating a holistic risk-assessment approach. Moreover, vulnerable groups such as children, older adults, and individuals with preexisting respiratory conditions are disproportionately affected by air pollution^11),(19. Consequently, the carcinogenic impact of these complex smoke mixtures is heightened in populations already facing health disparities or environmental stressors, resulting in a higher effective cancer risk due to both the nature of the exposure and the susceptibility of the affected population.

UV RADIATION: SUN EXPOSURE AND SKIN CANCER PREVALENCE

The Amazon's location near the Equator naturally exposes it to high levels of UV radiation, and recent research confirms that UV irradiance in the region is both intense and subject to seasonal peaks, especially during the dry season and around solar noon²². This intrinsic geographic factor, combined with growing human-induced environmental changes such as extensive deforestation, significantly increases direct population exposure to UV radiation. Occupational and environmental exposure to solar UV, particularly in equatorial regions like the Amazon, further elevates this risk, and global analyses estimate that nearly one-third of non-melanoma skin cancer deaths and disability-adjusted life years are attributable to UV exposure, especially among outdoor workers and older adults²³.

A short clinical-epidemiological study conducted in Manaus (Amazonas) between 2008 and 2018 with 543 patients confirmed that basal cell carcinoma was the most common type of skin cancer, accounting for 75.5% of cases, followed by squamous cell carcinoma at 18.1%. Most tumors (71.3%) were located on the head and neck, areas most exposed to sunlight, highlighting the strong association between UV radiation and skin-cancer incidence. Street cleaners, street vendors, and rural workers such as those in agriculture and fishing were identified as particularly vulnerable due to prolonged occupational exposure to sunlight. These findings reinforce the critical role of cumulative UV exposure in the development of non-melanoma skin cancers and underscore the need for targeted prevention strategies, particularly for high-risk occupational groups²⁴.

Although the Manaus study did not establish a definitive causal link between deforestation and increased UV exposure, it suggests a potential association that warrants attention. The observation that reduced forest cover diminishes natural shade indicates that individuals living and working in deforested areas, especially those spending considerable time outdoors, may experience more direct sunlight exposure. However, these findings should be interpreted cautiously, as multiple factors can influence UV exposure and skin-cancer risk. This example illustrates how environmental change driven by human activity could exacerbate natural risks, such as skin cancer in the Amazon, while emphasizing the need for further research to confirm these associations. It highlights the complex and interdependent pathways through which climate and environmental changes may impact health, underscoring the importance of cautious interpretation of current evidence.

HEAVY METALS AND CARCINOGENIC RISK: MERCURY, ARSENIC, AND THE FOOD WEB IN THE AMAZON

The Amazon is severely affected by heavy-metal contamination, primarily driven by illegal gold mining²⁵. This activity frequently employs mercury (Hg) for amalgamation, resulting in widespread pollution of aquatic environments. Consequently, fish populations - and, critically, human consumers, particularly Indigenous communities - are heavily impacted^26),(27.

Beyond Hg, other non-essential and highly toxic metals such as arsenic (As), cadmium (Cd), and lead (Pb), originating from industrial waste, domestic sewage, and agricultural fertilizers, also pose significant carcinogenic risks²⁸. These metals accumulate in ecosystems and human tissues, potentially leading to various cancers years after exposure²⁹. Cadmium exposure, particularly in occupational settings or through contaminated food and water, is associated with lung, breast, and prostate cancers, and can also cause kidney damage and other systemic effects^28),(30. The mechanisms underlying these risks include oxidative stress, DNA damage, impaired DNA repair, and genomic instability, which together drive the carcinogenic potential of these metals.

A study in the Cassiporé River basin, Amapá State, confirmed widespread contamination, reporting levels of chromium (Cr) and Hg exceeding safety thresholds in several fish species, as well as elevated concentrations of Cd, Cr, copper (Cu), Pb, and Hg in water samples. These concentrations represent a substantial health hazard to riverine populations that consume both contaminated water and fish³¹.

Carcinogenic risk may be amplified through trophic transfer and bioaccumulation within Amazonian food webs. The Cassiporé study suggested that carnivorous fish exhibited higher concentrations of Cd, Cu, Pb, and Hg, indicating a potential pattern of biomagnification. This finding implies that the risk is not limited to environmental presence but extends through the food web, potentially leading to higher toxin levels in organisms central to local diets, especially fish. Such accumulation may pose health concerns for human populations connected to these aquatic ecosystems, although further research is needed to clarify the long-term implications. The association between gold mining and fish contamination highlights an exposure pathway that warrants careful investigation³¹.

Flooding plays a critical role in exacerbating carcinogenic pathways by promoting the microbial conversion of inorganic Hg, often released by mining, into methylmercury (CH₃Hg⁺), a far more toxic and bioaccumulative form. The Cassiporé River study indicates that flood events, which are expected to become more frequent and intense due to climate change, significantly influence Hg and Cd concentrations in fish, thereby increasing health risks for local populations. In flooded wetlands, anoxic (oxygen-depleted) conditions and abundant organic matter create ideal environments for mercury-methylating bacteria, which rapidly transform inorganic Hg into CH₃Hg⁺⁽³². This process leads to elevated CH₃Hg⁺ levels in aquatic organisms, which then biomagnify up the food web, posing substantial neurotoxic and carcinogenic risks to humans who consume contaminated fish^33),(34. Research from various wetland and reservoir systems confirms that flooding, whether from natural events or human activities such as dam construction, can cause sharp increases in CH₃Hg⁺ production and bioaccumulation, with effects that persist for years^34),(35.

These findings suggest a potential link between environmental changes, such as increased flooding possibly related to climate change, and public health, especially in regions affected by heavy-metal contamination. While climate change may contribute to environmental stressors and affect the bioavailability and toxicity of existing carcinogens such as Hg, further research is required to establish a definitive connection between these factors. This potential interaction could increase health risks in the Amazonian environment; however, conclusions should be drawn cautiously until more evidence becomes available.

IMPACT OF FLOODS AND DROUGHTS ON HEALTH INFRASTRUCTURE AND ACCESS TO CANCER SERVICES

Extreme climate events in the Amazon, such as severe floods and prolonged droughts, are increasingly disrupting an already fragile health infrastructure, making it difficult for communities to access essential healthcare services, including cancer care that relies on timely and continuous treatment³⁶. These events can render roads impassable, interrupt river transport, the primary means of travel in many remote areas, and damage or isolate medical facilities, further limiting healthcare delivery. The compounded effects of climate change and environmental degradation intensify these challenges, as health systems are often under-resourced and ill-prepared for the scale and frequency of such disruptions³⁷. Indigenous and local communities have developed adaptive strategies, such as utilizing traditional knowledge and resource-sharing networks; however, official health responses often tend to be reactive and insufficient for achieving sustained resilience.

Cancer treatment is a complex, multi-phase process that typically involves access to diagnostics, surgery, chemotherapy, radiotherapy, and long-term follow-up. Floods may hinder patients' ability to reach healthcare facilities, and fluctuating river levels, combined with remote locations, can pose challenges for pharmaceutical logistics. These extreme weather events have the potential to disrupt the continuity of care, possibly leading to missed diagnoses, treatment delays, and issues with medication supply chains. Such disruptions could, in turn, influence health outcomes, potentially leading to more late-stage presentations and higher mortality rates. Strengthening climate resilience in Amazonian health systems might benefit from integrating Indigenous knowledge, improving infrastructure, training healthcare workers, and investing in emergency preparedness, though the extent of impact remains an area for further investigation³⁸. Without such measures, the growing frequency of extreme climate events will continue to undermine healthcare access and exacerbate health inequities, particularly for time-sensitive conditions like cancer^36)-(38.

VULNERABILITY OF INDIGENOUS AND TRADITIONAL POPULATIONS IN CANCER PREVENTION AND TREATMENT

Indigenous and traditional populations in the Amazon face profound vulnerabilities in cancer prevention and treatment due to a convergence of environmental, social, and systemic barriers. These communities experience higher rates of certain cancers, especially cervical cancer among women, who show a three- to fourfold increase in high-grade lesions and poorer access to screening and treatment compared to non-Indigenous women^39)-(40. Barriers include vast geographical distances, language and cultural differences, mistrust of health services, and a lack of culturally tailored care, which lead to delayed diagnoses and fragmented treatment^39),(41),(42. Even with specialized protocols, persistent challenges such as communication gaps and unprepared health professionals limit the effectiveness of interventions.

Environmental injustices, including exposure to carcinogens from contaminated water, air, and food, further elevate cancer risk, while climate-related disruptions can severely limit access to already scarce healthcare resources^40),(43. Community-based, intercultural strategies, such as involving Indigenous leaders, using native languages, and ensuring female healthcare providers, have shown promise in improving screening uptake and trust^41),(42),(44. Genetic studies also highlight unique cancer susceptibility profiles among Amazonian Indigenous peoples, underscoring the need for precision medicine and early diagnosis tailored to these populations^45),(46.

Overall, the cycle of environmental degradation, social inequality, and health-system inadequacy perpetuates unequal cancer outcomes, demanding integrated, culturally sensitive, and community-driven solutions.

REDEFINING HEALTH: THE INTRINSIC LINK BETWEEN HUMAN WELL-BEING AND ENVIRONMENTAL INTEGRITY (PLANETARY HEALTH)

The profound and undeniable connections between climate, environment, and cancer in the Amazon fundamentally challenge traditional, often anthropocentric, conceptions of health, those that separate human well-being from the health of the natural world. It becomes imperative to adopt a holistic Planetary Health perspective, which explicitly recognizes that human health and civilization depend on the flourishing of Earth's natural systems^37),(47.

A shift toward a Planetary Health perspective requires public health strategies to move beyond treating individual diseases and instead address the broader ecological determinants of health, factors rooted in the environment, society-nature relationships, technology, and material living conditions^48)-(50. Research highlights that human health is fundamentally dependent on the integrity of natural systems - clean air, water, food, and stable ecosystems - and that disruptions such as pollution, ecosystem degradation, and climate change directly increase disease risk and health inequities^48)-(50.

This approach aligns with bioethical frameworks that view health as a unity of body, spirit, and environment, emphasizing that well-being is shaped by both social and ecological contexts^48),(49. Despite longstanding recognition of these links, mainstream public health has often neglected ecological determinants, focusing instead on social or individual factors^49),(51. However, evidence shows that improvements in environmental quality, socioeconomic conditions, and sustainable practices can significantly reduce disease burden and improve population health^48),(50),(52. Integrating ecological determinants into health policy means considering the impacts of environmental change, resource use, and ecosystem services on health outcomes, and promoting sustainability as a core health practice^48),(53),(54.

This holistic view is particularly relevant in regions like the Amazon, where environmental and social systems are deeply intertwined and health depends on the resilience of both people and ecosystems. In the Amazon, where Indigenous and traditional populations are deeply connected to rivers, forests, and local ecosystems, this interdependence is especially significant. Potential carcinogenic risks from wildfire smoke, mercury-contaminated fish, and disruptions to cancer care due to extreme weather events illustrate how environmental deterioration can directly affect health. The Amazon could serve as a valuable example of Planetary Health, underscoring the importance of incorporating ecological well-being into public health policy and practice.

ENVIRONMENTAL JUSTICE AND THE UNEQUAL DISTRIBUTION OF RISKS: THE DISPROPORTIONATE BURDEN ON MARGINALIZED AMAZONIAN COMMUNITIES

The distribution of climate- and environment-related cancer risks in the Amazon is profoundly unequal, reflecting deep-rooted environmental injustices. Marginalized communities, particularly Indigenous peoples, riverine populations, and Afro-Brazilian rural groups (quilombolas), bear a disproportionate share of the negative impacts due to historical, socioeconomic, and political vulnerabilities^4),(55. Large-scale economic projects, often implemented without proper consultation or benefit-sharing, exacerbate these disparities by increasing exposure to carcinogens while simultaneously restricting access to healthcare.

Indigenous women in the Amazon experience heightened vulnerability to cervical cancer due to intersecting barriers such as geographic isolation, language differences, cultural misunderstandings, and inadequate healthcare infrastructure. These barriers are compounded by broader patterns of environmental racism and social inequality, which systematically expose marginalized populations to greater ecological hazards and health risks^56),(57. Structural racism and policy omissions, show that a disproportionate number of people living in extreme poverty reside in environmentally hazardous areas⁵⁸, while Black-Brown-Indigenous individuals are overrepresented among those affected by climate extremes, as high-temperature exposure⁵⁹.

Environmental racism in the Amazon is perpetuated by development models that prioritize resource extraction and economic gain over the health and rights of local populations, leading to persistent disparities in disease incidence, including cancer^56)-(58. These inequities are reinforced by inadequate public health services, long travel distances to care, and the absence of culturally appropriate interventions, all of which disproportionately affect Indigenous women and other vulnerable groups⁵⁷.

Addressing these disparities requires not only improved access to healthcare and culturally sensitive services but also structural changes that confront environmental racism and ensure fair treatment and meaningful participation of all affected communities in policy decisions^56)-(58.

Evidence indicates that systemic factors in the Amazon, such as legislative setbacks, extractive economic models, and infrastructural neglect, contribute to ongoing challenges including displacement of local populations, environmental degradation, and limited access to healthcare. These injustices are closely linked to health disparities, including rising cancer rates and difficulties in obtaining timely, effective treatment. The lack of basic sanitation and barriers to cancer screening and therapy illustrate how social and environmental determinants interact, potentially amplifying public health inequities.