I believe that at least 95% of human cancers have a viral origin (oncoviruses). In a report a while back in one of the science magazines found that EVERY oncogene (genes that cause cancer) that had ever been found were viral genes, and that no human oncogene had ever been found. In other words, they have never found a hereditary cancer in humans. Doctors routinely scare the people in to unnecessary tests and treatments by trying to convince them that cancer is hereditary and runs in families. This simply is not true 

Cancer viruses have been known since 1908 with the discovery of the avian sarcoma leukosis virus (ASLV) which causes lymphoma and leukemia in chickens. Two years later the first solid tumor virus, the Rous sarcoma virus, was discovered.

Since then many cancers have been linked to microbes, particularly viruses. For example Kaposi's sarcoma (KS), which actually has a bacterial form as well as a viral form. The viral form is caused from the virus human herpes virus type 8 (HHV8), also known as Kaposi's sarcoma-associated herpes virus (KSHV).

This fact was able to prove that AIDS did not originate in Africa. During the early years of AIDS it was found that the form of KS found in Africa was not showing up in the US. But the form of KS found in the US was showing up in Africa, showing a movement of AIDS from the US to Africa, not the other way around.

Here are some other examples of cancer causing viruses:

Human papilloma virus (HPV) linked to cervical, breast, prostate, penile, anal, nasopharyngeal and skin cancers.

Both the hepatitis B and hepatitis C viruses have been linked to liver cancer.

Epstein Barre Virus (EBV, also referred to as human herpes virus type 4) linked to Burkitt's lymphoma, Hodgkin's lymphoma, and nasopharyngeal carcinoma.

Then there are the human T-cell leukemia/lymphoma viruses 1, 2, 3 and 4, which cause various leukemias and lymphomas.

Herpes viruses have been linked to liver cancer.

Simian virus type 40 that contaminated the polio vaccines given to 90 million Americans has been linked to causes brain, bone, thyroid, and lymphatic cancers as well as mesothelioma.

I was posting on the Leukemia and Lymphoma Society board a while back and I got in to a discussion where I mentioned the viral origin of both leukemias and lymphomas. One poster made a comment about I should tell his doctor that since his doctor had never heard of leukemia/lymphoma viruses. So I told him to find a new doctor since these viruses have been well known in medicine for over 25 years in humans. Then I went to Medline and pulled up all sorts of abstracts on human leukemia and lymphoma viruses. Next thing I know I was not only banned from the board, but all of my messages were completely erased, and the posts calling me a quack were left up even though this was in direct violation of their posting policies. They were scarred of my posts because to admit that the cause of these cancers is known means that they have to admit that they are easily cured and therefore they would lose all their donations they were using to pay their salaries and to suppress the facts.

A great example of viral induced lymphoma was seen in David the “Bubble Boy”. David was born without an immune system and had to kept in a completely sterile environment. In an attempt to treat him for his immune deficiency the doctors decided to perform a bone marrow transplant. His sister was used as the bone marrow donor, but her marrow was not screened completely for viruses. David died from B cell lymphoma induced by the Epstein Barre’ virus contaminating her bone marrow.

Although viruses are responsible for the vast majority of cancers there are other microbal causes and in very rare cases parasitical involvement. Here are some examples:

Helicobacter pylori bacteria is linked to stomach cancer.

Aspergillus niger fungus produces aflatoxins linked to liver cancer.

Human liver fluke has been linked to liver (bile duct) cancer through its production of the hormone granulin, which promotes cellular division.

Radiation damage is also known to induce cancer. The US government proved this when they used unsuspecting people as human guinea pigs by deliberately releasing radioactive isotopes from the Hanford nuclear power plant, from 1944 through 1972, to test the effects on the general population. The radioactive iodine induced cancers and other illnesses in a number of people. Here is a link for those that don’t recall when this was exposed in the media during the mid 80s.

http://www.doh.wa.gov/hanford/publications/history/release.html

http://seattletimes.nwsource.com/html/localnews/2002252208_hanford25m.html?sy...

Another example of radiation induced cancer is lung cancer induced by radon. Radon is a gas produced by the decay of radium, which is a product of uranium decay. It is the leading cause of cancer among non-smokers. The radon seeps through the ground where uranium exists contaminating water and seeping in to houses built over the uranium deposits.

Carcinogens are considered another cause of cancer. This may be true in some cases, but I don’t believe that all carcinogens are actual cancer triggers. In some cases the carcinogens may only be cancer promoters. In particular compounds such as xenoestrogens. Not everyone exposed to xenoestrogens develop cancer. This could be explained by the xenoestrogens only promoting the growth of already existing cancers triggered by other sources such as viruses.