How does cancer kill?

50
Im only 15. I know a bit about cancer, but i cant find anywhere how it actually kills you. I understand metastasis; where the cancer spreads. But i dont understand how the growth of extra cells (damaged or not) can kill.

Might be a stupid question.

Staff: Mentor

No it's not at all a stupid question.

Here's a page that discusses it:

It looks like there are several ways discussed on that page:

• By preventing an affected organ from doing its normal tasks
• By blocking part of a lung, it can get infected
• By upsetting chemical balance - calcium, for example

50
Thanks very much, that cleared everything up. :)

4. blahlbah

1
why can't surgery just remove any potential threat then?? From what I understand, if a group of cancerous cells is not big enough to block a vital function, then you will not die.

Staff: Mentor

Sometimes the cancer is too well integrated into an organ to be removed without destroying the organ.

6. Moonbear

12,265
Staff Emeritus
Surgery is most successful with early detection, while the tumor is small and before it has a chance to metastasize (spread to other organs). Even then, it depends on where it is. Sometimes it's in a location where it can't be reached or safely removed by surgery.

7. bobze

652
To briefly add to this, it depends on the "type" of tumor as well. Not all tumors are nice little balls of cells waiting to be removed.

When cancer starts there are certain mutations that crop up in a kind of typical fashion. Or so most students learn, but in reality there isn't a set order that leads to neoplasm.

Some types of neoplasms turn out to be "spready" early only, that is to say they "migrate" away from home, because of the fortunes mutation has allotted them. Because of that, they end up seeding other places they land with new little cancerous colonies.

Glioblastoma (there is a topic about this over on the medical forums) and pancreatic adenocarcinoma are both examples of what we call in medical speak, highly invasive and aggressive neoplasms--That even with surgical resection typically have less than 5%, 5 year survival rates.

8. Pythagorean

4,622
cancer cells basically compete with your healthy cells. Your healthy cells are programmed to die under appropriate conditions to regulate constant, healthy cellular turnover. This process is called apoptosis. If your own body didn't kill it's own cells in a controlled way, it would start to build up a lot of dysfunctional cell populations, and overpopulation would put pressure on resource sharing. Cancer cells are cells that are no longer in touch with this aspect of the control system, but can still reproduce.

It seems that it's kind of an umbrella term for any disease that has this result (unregulated cell growth). The microscopic picture may not be the same for every case (my ignorance here, I'm just guessing there's more than one signaling pathway that can be the root cause of the emergent effect).

9. Curious3141

2,970
Others have already given many great examples, but here's a sample. The mechanisms by which a cancer can cause death can be classified like this (just a convenience classification, others are possible):

1) By becoming large enough to cause pressure-related complications locally. This applies especially to confined, anatomically critical locations like within the skull, so aggressive brain tumours (like glioblastoma multiforme) kill this way. Sometimes, even when there's space to grow, the tumour may obstruct the function of surrounding healthy cells and ducts, and cause a slower death that way, e.g. pancreatic cancer causing biliary system obstruction and all its attendant complications.

2) By causing systemic (body-wide) complications related to hormone-like effects. These are called "paraneoplastic syndromes". A serious one is related to a marked rise in serum calcium, that can have effects on the heart. Another serious one relates to an increase in clotting tendency, that can cause clots to form in the vascular system. The clots can travel to the vessels of the lung, a complication called pulmonary embolism, which can lead to compromised respiratory function and sudden death.

3) By compromising the immune system. This can happen directly, like in blood-cell cancers where the organs that generate immune system cells are directly shut down and the progenitor immune system cells are crowded out. It can also happen indirectly, like when chemotherapy given to cancer patients also hit healthy bystander immune cells, causing complications like neutropenia (markedly reduced numbers of a particular fraction of white blood cells) that can lead to a serious susceptibility to life-threatening infections.

Those are the main modes by which death occurs in cancer sufferers. Of course, rarer complications can always occur, for example in a large and friable (fragile) tumour, a piece can easily break off and block a large vessel or break into smaller pieces and embolise to the lung vessels. And sometimes cancers be associated with certain infections that can then cause further infectious complications. An interesting example of the latter is with a group of bacteria that are loosely known as Streptococcus bovis group, which have a tendency to cause colorectal (large intestine) cancers. The cancers themselves can also increase (by destroying the normally ordered tissue architecture) the likelihood that these bacteria migrate into the bloodstream (called translocation) and infect the heart's valves, resulting a severe infection called endocarditis, which can be life-threatening. But by-and-large, these are just interesting oddities that are nice to know about (unless you work in the field, as I do).

10. luben

71
A little diversion here. Is it true that the reason causing cancer is not well known? If we know the causes of cancer then in someday, we should be able to deliberately remove all these factors and stop cancer from happening.

11. Monique

4,699
Staff Emeritus
Cancer can arise due to many factors, a lot is known about it. The problem is that the factors are so diverse that taking them out is close to impossible. UV-radiation increases your chances of skin cancer, red meat of colon cancer, scolding-hot rice of mouth cancer, smoking of lung cancer etc. the list is very long. One can try to live healthy, but there is never a guarantee that cancer won't form. Aging is also a risk factor for cancer.

Staff: Mentor

We know a staggering amount about the causes of cancer. The problem is that both interaction with agents in the environment and non-perfect replication mean that DNA will inevitably mutate. Mutations in a variety of genes can accumulate and cause cancer. Trying to stop this is not a viable approach as you'll probably find that many mutagens are necessary for some aspect of health (such as UV exposure for vitamin D synthesis). Having said that simple lifestyle changes can reduce the chances of getting cancer e.g. not smoking and some factors can be immunised against e.g. the HPV vaccine.

What will make future cancer treatments more effective is early diagnosis, rapid genotyping of patient cancer and increased targeting/specificity of cancer cells.

13. bobze

652
You've guessed correctly :)

I'd also add to this, for the 'main ways cancer kills', is the release of endogenous substances. You're number 2 being more of a subset of the more general. Its not just hormones that cancers can release. Tumors undergo central necrosis that releases cytokines, pro-inflammatory molecules etc--Such that you can get a "cytokine storm-like syndrome" (see tumor lysis syndrome, searchable).

For instance in the heart of a necrotic tumor you have lots of things being released like TNF-$\alpha$, IL-1, IL-6 etc. These cause inflammation, hyperpyrexia, cachexia, etc. This can cause problems like you pointed out; of hypercalcemia or probably even more dangerous hyperkalemia (the body doesn't handle increased serum K+ well at all and this can quickly cause arrhythmia problems).

In deed Monique, if you live long enough--Cancer is a sure bet.

14. Telomere

3
There is no one universal cause that will always cause cancer in every individual so that when it is removed, cancer can be eradicated. Cancer is the result of a series of mutations in a single cell that continue to accumulate throughout every individual's life. There are many cancerous mutations constantly taking place in our bodies, but there is also a number of mechanisms which prevent the onset of a tumor (such as immune system). However cancer cells can sometimes "be smarter" than normal cells, meaning they can develop further mutations which then disguise them from our immune systems, enable them to grow their own blood vessels necessary for further growth and finally they develop additional mutations that allow them to metastasize to other parts of the body. Each step is a very complicated process. But unfortunately the longer a tumor grows, the more adaptable and cancerous it becomes so frequently cancer cells are so robust that it is impossible to kill them without killing their host as well.

15. Pythagorean

4,622
hrrm...

Looking back on this, I think what I described could also be a benign (non-cancerous) tumor. To be cancer it also has to be metastatic doesn't it? Is that the only difference between a tumor and cancer?

16. Telomere

3
Even though metastasis is one of the main characteristics of cancer, there are many more additional features that benign tumors do not have. To mention one of the many, cancer cells invade and destroy the tissue, which can often lead to organ failure, while benign tumors are separated from the surrounding tissue and often have a fibrous capsule which isolates them. Consequently they neither invade nor destroy the tissue and can only cause pressure on organs if they are big enough. Therefore they are not lethal (unless they are inoperable - e.g. some parts of the brain) and once removed they will not return.
BTW, not all cancerous tumors metastasize - for instance glioblastoma multiforme, one of the deadliest cancers known, almost never spreads to other parts of the body, but instead takes over the whole brain like an octopus resulting in coma and eventually death.

Last edited: Feb 15, 2012
17. MrRagnarok

16
And this is why, if one tries to remove the cancer with surgery or toxins, if even one cell escapes treatment that single microscopic cell will continue the cancer by replicating exponentially. This is another reason why it is so difficult to remove.

Staff: Mentor

Cells are not infected with cancer, cells become cancerous when they accumulate enough mutations to cause misregulation of cell division.