Presentations at the 14th Annual International Integrative Oncology conference recently shed light on the astounding connection between parasitic infections and cancer. New findings are bringing this discarded cancer hypothesis from the 1800s back into the scientific spotlight.
Medical Heretic…or Hero?
A Scottish pathologist by the name of William Russell was the first known individual to identify and record what he called a “cancer microbe,” in the year 1890. After examining cancer cells under a microscope, he found that they were infiltrated with what appeared to be spores of parasitic origin. Since that time, many other scientists have identified and recorded similar findings or made similar hypotheses regarding parasitic infections as a root cause of cancer. Yet these researchers and their ideas have generally been dismissed and some of them, such as William Russell, have even been viewed as “medical heretics.” Ironically, modern medicine and technology is one of the very things bringing this hypothesis to the surface once again. Let’s take a look at why this connection between parasites and cancer can no longer be ignored.
What Can Animals Tell Us?
The pathology of several different types of parasitic infections in animals has led to a better understanding of the link between parasites and cancer by identifying which signaling pathways are affected. In general, both cancer cells and parasite-infected cells exhibit these identical maladaptive behaviors: 1) inhibition of cell apoptosis/cell death and 2) the speeding up of cell replication. The tick-borne parasite, Theileria annulate, found in South African Cattle, has been shown to literally transform lymphocytes into lymphoma cells. Yet the disease is treatable with anti-parasitic medications.
In addition, a 2014 study of mice inoculated with the protozoan Cryptosporidium resulted in spontaneous development of colon cancer. The pathogenesis was linked to the infection-induced upregulation of the WNT signaling pathway, which has been previously linked to cancer. There is also conclusive evidence of at least 4 types of cancers in animals that have “evolved” into a transmissible parasite, including Tasmanian Devil facial tumor disease, Canine transmissible venereal tumor, Hamster-induced transmissible sarcoma, and Clam leukemia.
But is There Evidence in Humans?
The tick-borne bacterium borrelia (and its various forms) is sometimes referred to as a parasite, due to its symbiotic behavior inside the host. A link between borrelia infection and cancer has been reported on several occasions in the past decade or so. In 2004, this pathogen was implicated in 2 cases of nodal lymphoma. An article published in the journal Blood in 2008 reported that positive borrelia antibodies increased the risk of mantle cell lymphoma four-fold. And perhaps most intriguing were the 5 patients with Glioblastoma Multiforme treated at a Washington State clinic. All 5 tested positive for infection upon tumor biopsy and responded to treatment for parasitic disease. The tumors progressed when treatment was halted.
In 2015, Muehlenbachs et al published a case study describing a patient with human immunodeficiency virus (HIV) who presented with enlarged lymph nodes containing cells characteristic of cancer. When biopsied and tested using genomic analysis, the lymph node and lung tissue revealed tapeworm infection. This new discovery of a transformation from parasitic infection to malignant cancer in a human host is yet another example of the connection between the two pathologies. Since it has been previously been established that viruses can develop into cancer (ie. human papillomavirus (HPV) and cervical cancer; hepatitis C virus (HCV) and liver cancer), this finding should not be surprising to cancer researchers and physicians.
Anti-Parasitics to Treat Cancer?
Another consideration comes from looking at the current pharmaceutical treatments for cancer. Many anti-parasitic drugs have been repurposed as anti-cancer drugs. Here are a few examples:
- Artemisinin®/Ivermectin® – anti-malarial and anti-parasitic drugs that earned the doctors who discovered them a Nobel prize in 2015; have been extensively studied for their anti-cancer effects as well
- Vanquin® – common pinworm drug patented in 2009 for use in cancer; effective in treating blast cell leukemia, lymphoma, and breast cancer
- Niclide® – tapeworm medication patented in 2012 for metastatic cancer; works against colon cancer, osteosarcoma, and glioblastoma
- Alinia® – an anti-protozoal drug possessing a specific anti-cancer mechanism that beat out 5,000 other bioactive compounds; this effect was validated in animal studies
- Vermox® – anti-parasitic drug that out-performed 2,000 other medications in the treatment of malignant melanoma; can induce apoptosis and was shown to be better at permeating the blood brain barrier than a current medulloblastoma drug.
Conversely, some medications originally developed for chemotherapy have been used as anti-parasitics. The explanation for this interchangeability of treatments is the identification of several pathways that are involved in both parasitic infections and cancer. It would seem logical then, that these conditions would have overlapping causes as well.
As with any chronic disease, there are most likely many variables involved in the development of cancer. The case study of the patient with HIV suggests that the strength of the individual’s immune system plays a role, in addition to the pathogen itself. Even so, these findings collectively cannot be dismissed as coincidence and warrant further investigation. This is just a brief overview and only a few examples of the major arguments for this old hypothesis that is now supported by new evidence. Research in this area could potentially have a huge impact on prevention, diagnosis, and treatment of a disease that causes so much suffering and takes many lives all too soon.