Synopsis
Parasitic infections have been increasingly linked to cancer development. Parasites like Opisthorchis viverrini, Clonorchis sinensis, and Schistosoma haematobium have been associated with bile duct, bladder, and colorectal cancers, particularly in regions with poor sanitation and high parasite prevalence. The Plasmodium falciparum parasite, known for causing malaria, has also been linked to Burkitt lymphoma. Additionally, infections such as Strongyloides stercoralis and Chagas disease (Trypanosoma cruzi) have shown potential associations with increased cancer risk, particularly in patients with weakened immune systems or co-infections like HTLV-1. These parasites trigger inflammation, immune responses, and cellular damage, contributing to carcinogenesis.
Parasitic Infections and Cancer Risk
Cancer is a life-threatening disease caused by the uncontrolled growth of cells in the body. Similarly, parasites are harmful organisms that can sometimes be fatal. Both cancer cells and parasites share the ability to survive and multiply without external growth signals, resist programmed cell death (apoptosis), and evade the body’s immune defenses. These similarities make it difficult for the immune system to fully eliminate cancer cells and parasitic infections, posing significant challenges in treatment and eradication.
Parasites and Cancer Development
In vitro and animal studies have revealed that parasites can influence cancer development both directly and indirectly. While some parasites can promote cancer, others may trigger immune responses that exhibit antitumoral effects. Parasites can affect cancer progression by regulating immune responses, inhibiting metastasis, and angiogenesis, suppressing proliferative signals, and modulating inflammation, which can either stimulate or prevent cancer development. This dual role of parasites highlights their complex impact on cancer and the immune system.
Cancer-causing Parasites
Parasitic worms can increase the risk of cancer, especially for people who live in or travel across various high-risk zones globally. Opisthorchis viverrini and Clonorchis sinensis, liver flukes found in East Asia, are linked to bile duct cancer, primarily transmitted through consuming raw or undercooked freshwater fish. Schistosoma haematobium, found in parts of Africa, Asia, and the Middle East, is associated with bladder cancer. Ongoing research is exploring potential connections to other cancers as well.
Tapeworm Cancer Cells Linked to Tumors in Humans
Scientists at the Centers for Disease Control and Prevention (CDC) have discovered that cancer cells from the dwarf tapeworm (Hymenolepis nana) can cause cancer-like tumors in people with weakened immune systems. This marks the first documented case of a person falling ill from cancer cells originating in a parasite. The finding highlights the unique and rare ability of tapeworm-derived cancer cells to invade human tissue and form tumors, raising new concerns about parasitic infections.
Use Case: Unusual Cancer Discovery
In 2013, researchers diagnosed unusual biopsies from the lung tumors and lymph nodes of a 41-year-old HIV-positive man. The tumors resembled human cancer, but tests revealed the cells were not human. This discovery initiated a nearly three-year investigation into the cause of the man’s illness, eventually leading to the finding that the cancer-like cells originated from a parasitic tapeworm, not the patient himself.
Parasite-Induced Cancer: Ongoing Research
The link between parasitic infections and cancer development is well-established. However, further research is needed to identify the specific carcinogenic factors of parasites and the mechanisms through which they alter host signaling pathways or oncogenes to promote tumor growth. Understanding these processes is crucial for developing targeted treatments and improving outcomes for patients affected by parasite-induced cancers, as the complexity of these interactions continues to challenge current medical approaches.
Infectious Diseases and Cancer Risk
Six cancers—lung, liver, stomach, colorectal, breast, and esophagus—are the leading causes of cancer-related deaths. Four of these (liver, stomach, colorectal, and esophagus) are frequently linked to infectious diseases. Various factors contribute to carcinogenesis, as noted by the WHO. From 2008 to 2009, experts at the International Agency for Research on Cancer (IARC) reassessed and classified human carcinogens, categorizing infectious pathogens as significant contributors to cancer development. This highlights the complex relationship between infections and cancer risk.
Schistosomiasis and Cancer
Schistosomiasis is another parasitic infection linked to cancer, with risk factors often tied to environmental exposure. Studies have confirmed that this parasite can contribute to carcinogenesis, typically affecting the liver, colorectal region, and bladder. The link between schistosomiasis and cancer development highlights the importance of controlling environmental factors and improving sanitation to reduce the risk of infection and its potential long-term health consequences, including cancer.
Liver Flukes and Cholangiocarcinoma Risk
Opisthorchiasis and clonorchiasis, caused by liver flukes such as Opisthorchis viverrini and Clonorchis sinensis, affect over 45 million people worldwide. These parasites, prevalent in parts of Southeast Asia and East Asia, are linked to bile duct cancer (cholangiocarcinoma). The parasites invade bile ducts after consuming raw, infested fish, causing biliary fibrosis, inflammation, and cellular damage. Chronic infections, combined with other factors like genetics and liver diseases, increase the risk of cholangiocarcinoma, a highly aggressive cancer with limited treatment options.
Plasmodium Falciparum and Cancer Risk
Plasmodium falciparum, the most widespread protozoan parasite in malaria-endemic regions, enters the bloodstream by infecting and damaging red blood cells (erythrocytes). In addition to causing severe malaria, P. falciparum has been linked to Burkitt lymphoma, one of the fastest-growing human tumors. This connection is particularly notable in regions with high malaria prevalence, where the parasite’s impact on the immune system may contribute to the development of this aggressive cancer.
Strongyloides Stercoralis and Its Link to Cancer
Strongyloides stercoralis, an intestinal nematode, infects 50–100 million people in tropical and subtropical regions, causing strongyloidiasis. While half of infected individuals remain asymptomatic, severe cases can lead to gastrointestinal issues and hyperinfection syndrome, which is linked to high mortality. Studies have shown a connection between S. stercoralis infection and increased cancer risk, particularly in patients co-infected with HTLV-1, a virus associated with adult T-cell leukemia/lymphoma. S. stercoralis may enhance HTLV-1 replication, contributing to cancer development.
Chagas Disease and Its Association with Cancer
Chagas disease, caused by the protozoan Trypanosoma cruzi, is prevalent in South and Central America and has been linked to certain cancers. Studies have confirmed a connection between Chagas disease and gastrointestinal cancers, including esophageal leiomyosarcoma. One case-control study revealed that 27% of women with uterine leiomyoma were serologically positive for Chagas disease. Other reports also suggest a potential association between Chagas disease and colon cancer, highlighting its broader impact on cancer risk.
Conclusion
The connection between parasitic infections and cancer highlights the significant global health challenges, particularly in regions with poor sanitation and limited healthcare access. Parasites like Opisthorchis viverrini, Clonorchis sinensis, Schistosoma haematobium, and Plasmodium falciparum contribute to cancer through mechanisms like chronic inflammation, immune response modulation, and cellular damage. Understanding these processes is key to developing effective therapies. Travelers to high-risk areas should follow health guidelines to avoid exposure. Continued research into the link between parasites and cancer is essential for advancing prevention, early detection, and treatment options for those affected by these infections.
