ENVIROMENTAL CARCINOGENS

Exposure to environmental carcinogens is increasingly being recognized as part of the cancer puzzle, and the likelihood of being exposed to carcinogens in one's lifetime is high. A better understanding of environmental risks, such as those associated with an occupation, could lead to screening and a potentially earlier cancer diagnosis, suggest researchers writing in a review published online December 1, 2014, in the Open Journal of Oncology.

"One environmental risk factor that is currently and often flagged is if the patient currently smokes or is around someone that smokes often," write the authors, led by Dino Prato, NMD, from the Envita Medical Center, Scottsdale, Arizona. "One can hypothesize that if doctors could screen patients for environmental causes of cancer early, they may be able to inform the patient of the risks and essentially reduce the opportunity for the cancer to develop."

Tobacco, asbestos, and radiation are well-established carcinogens that the general public is aware of, but the authors point out that along with substances such as pesticides, metal ions, polycyclic aromatic hydrocarbons, and volatile organic compounds, pathogenic micro-organisms can also be added to the roster. And aside from well-researched viral pathogens, such as human papillomavirus, there is the potential for bacterial, trematode, and fungal causes of carcinogenesis.

In addition, micro-organisms can often create chromosomal instability by inserting DNA in oncogenes or tumor suppressor genes, through mechanisms associated with inflammation, or through toxin release. "Carcinogens are many times the root cause for cancer via genetic mutations," said study coauthor John Oertle, NMD, also from the Envita Medical Center. "A great example is how the human papillomavirus inserts itself into the DNA and mutates the cell."

"The genes we are born with don't cause cancer, it's the carcinogens, chemical toxins, and infections that turn on the switch, and most patients have never had this addressed in their treatment," he said in a statement.

The causes of cancer are complex and largely believed to be multifactorial — a confluence of environmental, genetic, and lifestyle influences. There has been more focus on environmental exposure in recent years, as in  a report issued in 2010 by the President's Cancer Panel. The panel noted that it was "particularly concerned to find that the true burden of environmentally induced cancer has been grossly underestimated." However, there was a decidedly mixed reaction to the panel's report; some experts and organizations applauded the effort and hailed it as a landmark document, whereas others were concerned that it overstated the risks.

Table. Carcinogen Classes and Common Associated Cancers 

Carcinogen	Cancer	Sources
Ultraviolet radiation	basal cell and squamous cell carcinoma, melanoma	Sun, tanning beds
Radon	leukemia, lymphoma, skin, thyroid, various sarcomas, lung, breast	soil
Asbestos	lung, mesothelioma, gastrointestinal, colorectal, throat, kidney, esophagus gallbladder	building insulation
Metal ions	lung, prostate, pancreas, renal	paint, batteries, stabilizing agent in plastic, chrome plating, welding, leather tanning, ferrochrome metals, electroplating, circuitry, electroforming
Organochlorines	breast, colorectal, pancreatic, prostrate, lung, oral/nasopharyngeal, thyroid, adrenal, lymphoma, gallbladder	pesticides, solvents
Polycyclic aromatic hydrocarbons	breast, skin, lung, bladder, gastrointestinal	cigarette smoke, vehicular exhaust, roofing tar, occupational settings, pharmaceuticals
Volatile organic compounds	lung, leukemia, and nasopharyngeal, lymphohematopoietic, sinonasal tumors	air, groundwater solvents, cigarette smoke, automobile emissions, and gasoline
Pesticides	breast, colorectal, pancreatic, prostrate, gallbladder	air, ground water, vegetation

A number of micro-organisms have been associated with the risk of developing a number of cancer types.

Viruses include Epstein–Barr, hepatitis B and C, human herpes virus 6 and 8, human papillomavirus, human T-cell leukemia virus type 1, and Merkel cell polyomavirus.

Bacteria include Borrelia burgdorferi, Chlamydia pneumoniae, Helicobacter pylori, Mycoplasma, Salmonella typhi-1, and Streptococcus bovis.

Also included are carcinogenic trematodes (Opisthorchis viverrini, Clonorchis sinensis, Schistosoma haematobium), which are most common in southeast Asia and sub-Saharan Africa, and Aspergillus flavusand Aspergillus parasiticus, which are fungi known for their production carcinogenic aflatoxin.

Increased Detection Needed

Some environmental carcinogens are avoidable, but others are more ubiquitous and can be difficult, if not impossible, to avoid, note the authors. But after thorough testing, key carcinogens that caused or contributed to the cancer and genetic mutations can be identified in some cases.

Thus, they write, it is important for physicians to recognize if a cancer patient is still being exposed to the same carcinogens that potentially caused the cancer, it could be causing further damage to the body.

In addition, detecting and recognizing microbial and trematode infections associated with cancer risk could serve as an early warning to physicians, that these carry an elevated risk for oncogenesis, the authors point out.

"Awareness of the risk factors associated with cancer causation by understanding the environmental risk factors is important for the doctor but is also important for the people who might be exposed to these carcinogens," they conclude.

The authors have disclosed no relevant financial relationships.

Open Journal of Oncology. Published online December 1, 2014.  Abstract