When people talk about illness, they tend to say they have lung cancer instead of lung tumours, or brain tumours instead of brain cancer. Why is this?
Tumors in the lung are much more likely to be cancerous than a tumor in the brain. Further, the lung is much easier to biopsy than the brain, so you're much more likely to know for sure that a lung tumor is cancerous than a brain tumor.
I think people are just being accurate. When they know the tumors in their lungs are cancerous, they accurately refer to it as "lung cancer" or "cancer of the lung". When they have one or more tumors in their brain and are not sure the tumors are cancerous, they accurately refer to it as a "brain tumor". You certainly do hear the term "brain cancer", and it's generally used when one knows the tumors are cancerous.
For example, if someone says "I have a pituitary tumor", that means that they have a tumor in (or on) their pituitary gland. Likely they don't know if it's cancerous, and often they're non-cancerous.
A person with hamartoma of the lung has one or more lung tumors. But they do not have lung cancer.
I am not a doctor, but!
A tumour has to be malignant to be called a cancer.
Lungs may have a few small tumours without affecting the quality of life at all (depending on the locations of the tumours, of course). I suppose people may have some lung tumours without ever knowing about them.
Even a small tumour in the brain is more likely to have very adverse effects. Impaired cognition, paralysis and hormone imbalances are just a few examples. A brain tumour is bad enough even if isn't cancerous. The number of people with brain cancer is a small subset of the people with brain tumour. I guess this is why you've heard "brain tumour" more often than "brain cancer".
Others have pointed the possibility of a tumor not being necessarily cancerous. I would have thought that another difference is that a tumor is always localized to a small part of the body, but cancer can (and unfortunately often will) spread out. Lung cancer at least has the tendency not to be confined to a small part of the lung.
The difference is, of course, even clearer in the case of leukemia.
On a neuroscience perspective, cancer cells are carcinogenic, often characterized by metastasis, pervading throughout the human body. These cancer cells are often malign and estranged to human body. On the other hand, tumors come in either lenient, innocuous form or malign, detrimental form. In some health conditions, doctors would only give recommendation for a patient to undergo an operation, until the cancer cells already incur severe damage to a particular body organ.
If the tumor doesn't lead to cell mutation, or noticeable physiological changes, the doctor will not give the recommendation for a surgery or any forms of treatment.It seems common for individuals to have certain forms of tumors these days without receiving a treatment, because some tumors are innocuous to be left untreated. A person needs to get tested to see if the tumor is positive or negative.
So for cancers, most cancer cells are metastatic and often uncontrollably propagate to the rest of the body organs. The earlier the detection, the more promising the results. It's unlikely cancer cells can be left untouched. Even after chemo and operations, cancer cells share a common feature to retrogress.
in general, cancer cells and tumor cells mutate and differ in their severity in damaging human body, so one shouldn't mix up a tumor with a cancer.