carcinogen update, now including H Pylori

 The NIH/National Toxicology Program recent Report on Carcinogens (RoC), mandated by congress, has an updated carcinogen list just published with hyperlinks to background documents: https://ntp.niehs.nih.gov/whatwestudy/assessments/cancer/completed/ . the National Institute of Environmental Health Services of the NIH also has an alphabetical list in their 15^th report (see https://ntp.niehs.nih.gov/ntp/roc/content/listed_substances_508.pdf ). It is notable in these reports that (finally) H Pylori has made it onto the lists as a new member of the crew. I am bringing the H pylori aspect up now, since there are many newer blog readers who may not have seen the plethora of my old blogs on H Pylori (see http://gmodestmedblogs.blogspot.com/search?q=h+pylori ), which make the following points:

 

1.       H Pylori is the most prevalent bacterial infection in the world, more than 50% of people are infected

2.       Both symptomatic and asymptomatic cases are associated with increased risk of gastric cancers: H Pylori worldwide is associated with 780,000 new cancer cases annually, 6.2% of all cancer cases

3.       Studies have shown that detecting and treating symptomatic or asymptomatic cases leads to decreased subsequent cancer risk

4.       There are some variants that are more aggressive than others (CagA is associated with higher likelihood of duodenal ulcers as well as precancerous lesions and gastric cancer, see http://gmodestmedblogs.blogspot.com/2018/01/h-pylori-ppi-use-and-gastric-cancer.html ; VacA strain is actually associated with colorectal cancer). Testing for variants is not available to us clinicians, though these may well explain some of the divergence between H pylori prevalence and gastric cancer incidence in some areas

5.       H Pylori is found pretty frequently in the US. Several studies, including the 3^rd NHANES, have found H Pylori in around 30-40% of people here (eg see http://gmodestmedblogs.blogspot.com/2019/12/h-pylori-in-us-veterans.html which references other studies)

6.      There is also argument that it might be appropriate to screen people who are on regular NSAIDs: studies have found that the risk of GI bleeding (including major bleeds) in patients on NSAIDs is much higher when they have untreated H Pylori infection (eg see http://gmodestmedblogs.blogspot.com/2015/05/h-pylori-and-nsaids-increased-gi.html ). Again, treatment lowers the risk.

-- I personally do regular screening of my patients and have found both symptomatic and asymptomatic H Pylori in many who have never traveled out of the US. A few of the unusual symptomatic cases: a man who had never left the US who had steroid-resistant ITP and was scheduled for splenectomy, but then tested positive for H Pylori, was treated, and the ITP vanished in a matter of days after treatment!!!; another with chronic pruritus whose pruritus also resolved with H Pylori treatment (for a review of derm manifestations of H Pylori, see hpylori and skin disease amjclinderm2002 in dropbox, or Wedi B. Am J Clin Dermatol. 2002; 3(4): 273.).  i should add that H Pylori screening is not recommended routinely in the US, and i am more focused on it because of my large immigrant population. Nonetheless i have found several US non-travelers with infection.

-- However, one could easily argue the following: the incidence of gastric cancer is low in the US even though there seems to be a significant H Pylori prevalence (though this prevalence should be validated in different populations in different areas of the US), so why worry?? And maybe we should focus on immigrants from countries where both H Pylori and gastric cancer are common (eg several Central American countries: Dominican Republic, Haiti, Jamaica, Guatemala..., as well as many other areas of the world (see https://www.wcrf.org/dietandcancer/stomach-cancer-statistics/ for gastric cancer incidence in different countries).Maybe the cases in the US are less likely to have the CagA variant?? Maybe other conditions in the US (foods eaten, less salt, other factors??) might decrease the carcinogenicity of H Pylori??

-- and, though this infection is all over the place, there are lots of unanswered simple questions: 

    -- how is it transmitted?? seems more common in densely populated lower SES countries, and most people with it get it by age 10 (though, in the US the number of cases detected increases with age). is this because they got it when young and grew up with it, but younger people now get it less because of ??better sanitation ??better housing conditions, with less density of housing ????not sure any of this is true...). and, the major reservoir for H pylori seems to be humans. is it spread by fecal-oral route/contaminated water (as hepatitis A, etc)? and/or by direct person-person transmission?? perhaps from animals (eg domestic cats may be a vector. other nonhuman primates?). Many unknowns, which is a pretty striking for such a widespread carcinogen that has been known for decades (and genetic analyses suggest it's been around for 58,000 years)

    -- why is reinfection after treatment so rare? immunology? just that those treated are older and less likely to get it again, since there is less infection in older people (for whatever reason)???

Further commentary:

-- The other carcinogens in the RoC documents are largely chemicals used in industry, some medications (eg azathioprine), some other viruses (eg EBV, hepatitis B and C, HPV, HIV), and alcohol/tobacco. And huge numbers of other chemicals (almost all industrial) are listed in the "reasonably anticipated to be human carcinogens"

-- it all makes one wonder if our great advances in treatments for diabetes, heart disease, cancers etc, etc are largely just compensating for the large increases in adverse socially-mediated issues creating so much disease. are huge improvements in meds for diabetes largely just compensating for the increased levels of obesity, eating unhealthy foods (often with more and more chemical additives) and getting less exercise? Similarly for cardiovascular disease? and are improvements in breast cancer therapy being partially offset by increases in carcinogens in the atmosphere (eg, PCBs??) and higher likelihood of developing of breast cancer? and what about the increasing incidence of pancreatic cancer: is that related to environmental chemicals (see http://gmodestmedblogs.blogspot.com/2021/12/pancreatic-cancer-increasing-incidence.html )?

so, a remarkably brief blog (from my standards), but i do think it should give us pause...

-- H pylori is such a huge international problem, and so many of our patients have either come from or travel extensively to countries of very high H pylori prevalence (and concomitantly high prevalence of gastric cancer), that testing/treating should be on our radar screens. and perhaps more so for non-immigrants as well??

-- i think there have been such profound changes/contaminations throughout our environment (water, air, soil, food we eat, etc) from the multitude (thousands and thousands) of new untested or minimally tested industrial chemicals introduced into the environment annually, as well as the well-known ones of the past (lead, dry cleaning chemicals, vinyl chloride,  asbestos....  see the extensive list of known carcinogens in the documents above, and these only make the list when they have been around a long time and have blatant associations with cancer.....  the new ones will need to wait for more bad outcomes.)

-- we as clinicians and public health advocates do really need to deal politically with the issue of protecting our environment.  for example, we should be more careful in prescribing antibiotics for unclear indications (viral respiratory illnesses, etc) in order to decrease the development of antibiotic-resistant microbes. We do have an important role, but the dominant issue is the overuse of antibiotics in industrial farming (estimates vary, but up to 80% or so of antibiotics goes to livestock for human consumption, a truly large source for the development of antibiotic-resistant microbes, eg see http://gmodestmedblogs.blogspot.com/2018/04/antibiotic-overuse-in-animals-and.html).  And, we should also be front and center in advocating for the importance of clean water, air, food supply as a fundamental public health principle, requiring much more regulation and control of industrial chemical development and use...

geoff

 

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