Does a pathogen cause cancer

Answer 1

Short Answer:

Cancer is, of course, not a single disease and there are hundreds of diseases which are deemed to be a type of cancer. Of those many forms of cancer, there are some which are known to be linked to particular pathogens, i.e. some kind of infection agent, such as a virus or a bacteria, is known to be the "cause" of the cancer. It is highly uncertain, but (see link below) it has been estimated that around 20% of cancers are connected to, if not caused by, a pathogen.

Additional Comments:

Perhaps the most well known cancer causing pathogen is the Human papillomavirus (HPV). This is the reason women get PAP smears as a method of testing for Cervical cancer. HPV is sexually transmitted and extremely common. While true, this characterization of HPV and cancer is grossly over simplified. There are over a hundred types in the family of papillomaviruses, two are associated with 70% of HPV caused cancers. HPV cancers can occur in other locations than the cervix and occur in men and women. While sexual transmission is typical, there are over modes of transmission. Most men and women have been infected by some papillomavirus, but often the infection is temporary. Recently, a vaccine which is reasonably effective for some of the most threatening types of HPV has become available for women who have never been infected. The vaccine has potential benefits for men, but it is less clearly assessed.

While HPV may be well known because sex and cancer are clearly topics of popular interest, the wider topic of all pathogen-induced cancers is much larger and much more important and is also a subject for much research funding.

The idea that a particular pathogen causes a particular cancer is a simplistic idea that can lead the the false notion that cancer can be treated like an infection disease. That is not how it works. Of course, there is a lot about cancer that is unknown. In most cases where a pathogen is connected with a cancer, the pathogen may not be causing the cancer, but may be diverting or inhibiting the natural defenses of the body that are able to intercept and neutralize damaged cells which could lead to cancer. Indeed, cancer caused by radiation and chemicals are usually examples of agents that cause cell damage that can not be repaired fast enough and therefor permit damaged cells to evolve to clinical forms of cancer. So, prevent the body from carrying out natural processes of repair is itself enough to allow cancer to develop.

Generally, cancer is a process where otherwise normal cells begin to divide and grow in an abnormal fashion. Sometimes, that happens by accident, i.e. defective cells occur all the time and they die naturally or just hang around being defective, but the body has developed complex cellular processes that detects such defects and repairs them, kills them or isolates them. When those processes fail to detect a certain kind of malignant cell growth or the processes are just unable to do an adequate repair, the avenue for uncontrolled cell growth and cancer become available.