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Several fact-sheets and web-sites claim the cause of stomach cancer is unknown:

The exact cause of stomach cancer is unknown,

The exact cause of stomach cancer is unknown,

Even though the exact cause of stomach cancer is unknown,

These sites go on to list some of the risk factors that are associated with a higher chance of stomach cancer, including:

  • gastritis (stomach inflammation)
  • pernicious anemia
  • gastric polyps, and
  • gastric (peptic) ulcer.

(amongst many others)

Is the cause of stomach cancer known?

  • What makes you skeptical that it isn't? What would conastitute a convincing answer? – Reinstate Monica iamnotmaynard Nov 14 '14 at 20:08
  • In Japan it is "common knowledge" that Helicobacter pylori causes 90% of stomach cancer, although that linked paper says 40% in men. – Ken Y-N Nov 18 '14 at 1:39
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    "The cause" assumes there can be only one. There may be many. If the question is about knowing any causes it should be reworded to say something like "are any [or most] of the causes of stomach cancer known?" – matt_black Apr 29 '16 at 12:49
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Cancer is not a single disease, but the term for a range of different diseases with the same ultimate symptom: cells that grow in an uncontrolled manner and which can invade other tissues.

Cancers can be caused by a huge array of environmental factors, but the tissue type where the cancer occurs will have different levels of environmental exposure. Damage by UV radiation, for example, is a common cause of skin cancer, but almost for cancers of internal tissues such as the ovaries, because the skin is the only tissue which is exposed to UV from sunlight.

In the case of stomach cancer, a variety of environmental cues suggest themselves, including diet and certain infections. However, it's impossible to pin down a single cause of stomach cancer, just like it's impossible to pin down a single cause for almost any cancer. The possible range of causes is too diverse.

So the literal answer is that yes, the cause of stomach cancer is unknown. But the question itself is not terribly meaningful.

EDIT: The OP asked if this meant there was no way of tracing a specific individual cancer back to its cause.

Not really - my apologies for a poor explanation of my point. The problem is more one of how things are grouped and classified. It's possible in occasional cases to discover the originial cause of a specific instance of cancer (the reasons why deserve an answer in themselves) - but because different individuals presenting stomach might have different root causes, you can't say that stomach cancer has a single cause.

Here's an analogy. Imagine there's an interruption to the internet service to your house. If it's short, you'll probably never know (or care) what the root cause is. But if not, there could be lots of reasons. Your router could be faulty. There could be a power out at the local exchange. An important pylon somewhere might have blown down in a storm. A shark might have chowed down on a vital ocean cable.

The question about stomach cancer is akin to asking "is the cause of internet outages known?" as though there's only one possible cause when there are many. And each individual instance can likely be traced to one of a number of different causes.

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    Hello, you need to post references to answer on this site. See meta.skeptics.stackexchange.com/questions/1505/… – Sklivvz Nov 14 '14 at 18:19
  • Thanks for adding the references in. To show I've understood: you are saying there are several known potential triggers for cancer, but no way of tracing a specific individual cancer back to its cause and therefore "the cause of [this particular] stomach cancer is unknown." Is that a fair summary? – Oddthinking Nov 19 '14 at 14:53
  • @Oddthinking No problem. See my edit. Hope it's helpful. – Bob Tway Nov 19 '14 at 16:06
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    I am a big fan of the "cancer is not one disease" mantra, however I would have to disagree with this answer. Saying that the cause is unknown means that there is no known cause. The fact that every cancer is different does not in any way imply that the cause is unknown, just that there are multiple causes. You are already naming diet and infections, so, here are some known causes... – nico Nov 19 '14 at 16:07
  • @nico Quite - but that's not what the OP is actually asking. My answer is an attempt to clarify why the way the question is phrased makes it relatively meaningless. – Bob Tway Nov 19 '14 at 16:08

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