There is much written about the cause of cancer, and many issues are controversial or unresolved. Nevertheless, certain patterns emerge and various aspects are discussed below.
Nature Gone Bad
It is surprising that something as terrible as cancer can arise from such a natural life process as growth. Cancers are not foreign matter in the body, but simply too many body cells growing too quickly. Although there is much discussion and controversy about toxins and radiations as the "causes" of cancer, in fact these are at most only a trigger that starts cancer. Once started, the body simply follows its normal growth sequence, though it does so far too quickly, and removing any toxins or radiation does not stop the cancer. There is nothing toxic or foreign inside tumor cells. Instead, something happens naturally within the body's make-up that allows cancers once started to keep growing.
In fact, for a solid tumor to take hold and spread, it actually has to do several tasks. Firstly, it has to grow too quickly. Secondly, it has to create substances that allow it to penetrate blood vessels, in order to get access to a blood supply to enable it to get the nutrients that allow it to grow. Thirdly, it needs to be able to penetrate into tissues so that when it spreads, it takes hold in a new site and grows again.
That all these processes take place by chance seems highly unlikely. There is something innate within the human body that makes all these processes possible. Somehow, the human body is programmed to help cancers.
Triggers of Cancers
There are many environmental or toxic substances that have been suggested as triggers for cancer. Below is a list of various cited triggers of cancer, although some of these may be controversial, and may even found to be incorrect.
- Radiation: it is well established that some forms of radiation
can cause particular cancers.
There remains must controversy about the effect of radiation emissions
such as power lines, cell phones, and so on.
The most commonly accepted associations between radiation
and cancer include:
- Sunlight and skin cancer (especially UV light)
- Nuclear radiation (esp. X-rays) and leukemia (and other cancers)
- Chemical toxins: Whether particular substance cause cancer
is always a hugely controversial issue.
Nevertheless, some links are widely accepted.
Some of the most commonly accepted associations between chemicals
and cancer include:
- Tobacco (tar) and lung cancer
- Asbestos and mesothelioma
- Betel nut chewing and mouth cancer in India
- Aflatoxin (in mold) and liver cancer in Africa
- Trauma and injury: some cancers seem to grow at the sites of injuries ranging from major trauma to the sites of bruises. This would be consistent with a cancer occurring from an error during the rapid-growth phase of healing. Some examples that have been examined include: head trauma, gallbladder cancer from gallstones, bone sarcomas (in old scars).
- Infection and inflammation sites: a cancer can occur at
the site of a previous infection or inflammation.
This would make sense if the healing causes rapid growth in this area
that might be subject to more frequent errors.
Another possible mechanism
is that inflammation also releases substances that are oxidants,
perhaps leading to higher oxidative damage to DNA.
As an example, the relationship between sexual viruses and cervical
cancer may not be the virus itself, but either the healing that occurs
after the virus has inflamed the cervix site,
or the substances from the inflammation reaction.
There are also examples of links between bacteria and parasitic infections and cancers,
which may well be due to the resulting infections and inflammation.
Some of the cancers linked with associations to
chronic irritations are:
- Anal cancer: fistulas, fissures, inflamed hemorrhoids, genital warts, scars, infections (chlamydia, trichomonas, herpes, gonorrhea, dermatitis)
- Bile duct cancer: ulcerative colitis
- Colon cancer/rectal cancer: inflammatory bowel diseases (e.g. Crohn's disease, ulcerative colitis)
- Esophagus cancer and gastric reflux, gastric damage from hot beverages, and lye ingestion.
- Gall bladder cancer and gallstones (an amazing 85% of gall bladder cancer patients had gallstones), calcified gall bladder
- Oral cancers and poorly fitting dentures or broken teeth (causing irritation)
- Kidney cancer and polycystic kidneys
- Liver cancer (including liver angiosarcoma) is associated with liver cell damage from iron overload (haemochromatosis)
- Pancreatic cancer and chronic pancreatitis
- Bone sarcomas and fractures, chronic bone infection, and Paget's disease.
- Small intestine cancer and gastrointestinal disorders (IBD, Crohn's, etc.); also a strange feature that Helicobacter pylori infections can lead to lymphoma.
- Stomach cancer and gastric reflux, Helicobacter pylori, peptic ulcer, and pernicious anemia
- Thyroid cancer and goiter from iodine deficiency, and Hashimoto's thyroiditis
This association between infection/inflammation sites and cancer could have causality in either direction, or both. Perhaps some infections and inflammations lead to cancers. On the other hand, perhaps some cancers lead to inflammations, because the immune system tries to get rid of a tumor, and so the association arises from the reverse causal direction.
- Anatomical or Congenital abnormality: several types of cancers
are increased if there is a physical abnormality
of the organ or system.
This may be due to a secondary inflammation being caused,
or some other mechanism.
- bile duct cancer and bile duct abnormalities
- testical cancer and an undescended testical (10% of these cancers)
- esophagus cancer and chronic stricture such as muscle spasm (achalasia)
- melanoma skin cancers and moles on the skin
- thryoid cancer and chronic TSH elevation from a congenital defect
- Colon cancer and colon polyps
- Fetal remnants: some tumors seem to arise at sites within the body where there is a misplaced cellular remnant from embryonic and fetal growth. (It is unclear whether this is supported by research, or merely anecdotal observations.)
Note that some of these associations are not necessarily that useful. For example, although it is possible that moles lead to melanoma and polyps to colon cancer, it might also be that the association arises because the early stages of a cancer growth causes these anatomical changes: pre-melanoma causes moles, or colon pre-cancer causes polyps. However, the effects of undescended testicle or fetal remnants are interesting.
- Viruses: There are several cancers that seem to
have a viral trigger.
However, these seem to be a minority of cancers,
and cancer is almost certainly not a purely viral disease.
The cancers and viruses on this list include:
- Human papilloma virus (HPV) and cervical cancer, vaginal cancer, or vulval cancer.
- Human T-cell leukemia/lymphoma virus-1 (HTLV-1) and some types of leukemias and lymphomas; about 5% of people with HTLV-1 get cancer.
- Hepatitis B virus (HBV) and liver cancer
- Nasopharyngeal tumors and the Epstein-Barr virus (EBV)
- Burkitt's lymphoma and EBV
- Kaposi Sarcoma and Herpes Virus 8 (HV8; also called KSHV) or cytomegalovirus, but the link is unclear; the link between KS and HIV is only secondary and due to immune suppression.
- (a) viruses might inject viral DNA into human cells and create tumor cells this way. One likely method is that virus DNA may contain oncogenes or genes that suppress anti-cancer human tumor suppressor genes. For example, HPV genes secretes proteins E7 and E6 that block some tumor suppress genes: E7 blocks RB; E6 blocks p53. HTLV-1 secretes a protein called Tax that binds to a chromosome replication error checking protein called Mitotic Arrest Defective (MAD), thus making DNA errors more likely during cell division.
- (b) viruses might simply cause DNA mutations through DNA damage;
- (c) viruses might merely indirectly cause cancer because they create an infection and inflammation in the site, causing rapid cell growth from healing, and a tumor appears from this indirect route; the relationship between particular viruses and types of tumors might simply be that they usually inhabit the particular cell types or body areas.
Viruses might well use a combination of methods. Perhaps all viruses use a combination, or some viruses use one method and other viruses use other methods.
- Immune suppression: a weakening or total suppression of the immune
system seems to cause certain cancers.
Certain cancers are common to AIDS patients,
those on immune suppression
anti-rejection drugs for transplants,
or subject to other immune degradation (tuberculosis,
blood vessel vasculitis, lupus, EBV, and other causes).
Examples of cancers common in immune suppression:
- Kaposi Sarcoma
- lymphoma (certain types: primary CNS lymphoma),
- cervical cancer,
- brain cancer (certain types).
- skin cancer (basal/squamous cell)
- thymus (thymoma)
Although some cancers increase, not all cancers are common to the immune-suppressed, leading to the conclusion that not all cancers are naturally protected by immunity.
- DNA repair errors: although very rare,
some genetic defects can block the body's ability
to repair DNA errors.
This makes DNA repair errors more likely,
increasing the chance of a cancerous mutation.
- Xeroderma pigmentosum (XP) occurs when the body's enzyme that repairs DNA damage from UV light is disabled, leading to skin and other cancers.
- Dietary insufficiency: There are some relationships between dietary deficiencies and cancers. The evidence seems largely incomplete, and perhaps the associations arise because people who have dietary deficiencies also have other difficulties. (Is there more than anecdotal evidence here?)
- Hormones: Female hormone cycles seem to be strongly indicated in breast cancer and ovarian cancer. Testosterone seems needed for prostate cancer and also for BPH, and testosterone levels also affect an existing prostate tumor.
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