Prostate cancer cells.
This entry is part 21 of 22 in the series Science Surgery
Our Science Surgery series answers your cancer science questions.
Pat asked: ‘Are benign tumours different from cancerous tumours?’
“This is a question we are often asked by patients,” says Dr Stuart Smith, a neurosurgeon and researcher at the University of Nottingham. “The answer depends on how you define it, and it will differ from doctor to doctor and from scientist to scientist.”
Smith says that in general, cancerous, or malignant, tumours would grow quicker than a benign tumour. “They’re more active. They tend to spread more through the tissue locally and, generally, they also have the ability to spread to other regions of the body, through the blood or lymph nodes.”
Smith says he often gives his patients the example of a mole on the skin, which is a benign tumour, and compares this to a melanoma, which is a malignant version of a mole.
But Smith says the definition is less clear cut in his area of expertise, brain tumours. “Even with the most malignant, fastest growing brain tumours, it’s pretty rare for them to spread elsewhere in the body.”
These tumours tend not to spread to the lungs, the liver or the bone, like other cancers do. Instead, they grow very quickly, spreading in a stepwise manner, rather than jumping to the other end of the body.
Smith says that brain tumours are quite a diverse group. One example is a tumour that grows in the lining of the brain, called a meningioma. They’re very common, but for most people they’re quite benign and are picked up almost by accident, on scans people have for other reasons. “Like a mole on the skin, they often don’t require any treatment or intervention.”
But that’s not true of all meningiomas. Or all brain tumours.
“A lot of brain tumours sit in a slightly grey area where they do grow, and they do invade the brain, but they do it in a slower fashion. They exhibit some of the characteristics of malignant tumours, but not all of them.”
The big problem for Smith is that these tumours can still be life-threatening. “If someone is dying from a tumour, then it’s not benign for that individual.”
High versus low grade
For this reason, Smith explains, brain tumour patient groups prefer not to use the terms ‘benign’ and ‘malignant’.
“We tend to describe them as either low-grade or high-grade, rather than necessarily saying they’re benign or malignant.”
Brain tumours are graded from 1 to 4. In general, grade 1 tumours are slower growing and invade less aggressively. Grade 4 are the fastest-growing, most aggressive tumours. Grades 2 and 3 are somewhere in between.
“There’s a continuum of behaviours between the low-grade tumours and the very high-grade tumours,” Dr Smith adds. “So, it’s very hard to say that grade 1 tumours are benign.
If a grade one tumour isn’t removed, then it will grow. “And, if a grade one tumour is in the brain stem, for example, and it keeps growing and can’t be completely removed or effectively treated with radiation or chemotherapy, then it can kill somebody.”
Scientists don’t know for sure why brain tumours are different in this regard to other types of cancer, but some theories exist.
“It’s probably something to do with the cells from brain tumours having difficulty establishing themselves outside of the nervous system,” says Smith.
“The other issue perhaps is for tumours like glioblastoma where, unfortunately, because the survival for a lot of patients is so bad, the tumour doesn’t have time to establish itself outside of the nervous system and the patient dies of brain disease before it spreads.”
When cancer spreads
This ability of cancer to spread, either locally or around the body, has important implications for how it can be treated, as Smith explains. “In general for tumours, the more localised they are, the easier they are to treat, either with surgery or radiotherapy. That holds true for cancer in any part of the body.”
Take melanoma for example. “If you have a melanoma that hasn’t spread beyond your arm, it can be treated with surgery and that can be very successful and cure the disease.”
The same is true for some brain tumours, in particular lower grade tumours found in parts of the brain where the tumour can be completely removed by surgery.
“With the higher-grade tumours, particularly the grade three and four tumours, inevitably the tumour has already spread quite widely within the brain,” says Smith. For these tumours, completely removing the tumour is no longer possible and the only approach is radiotherapy and chemotherapy to try and keep the seedling tumours that are left behind under control.
“Unfortunately, at the moment, those treatments aren’t good enough to eradicate the seedling tumours that are left behind in the normal brain,” says Smith. “Inevitably after a period of time, those seedlings develop into fresh tumours and that’s a problem.”
Searching for solutions
Smith’s research aims to tackle this issue in two ways.
“My research is in a type of brain tumour called glioma, which can occur in any age, so I look at childhood gliomas and gliomas that occur in adults.”
The first approach is to better understand the biology of brain tumours in the hopes of finding new types of treatment.
“A lot of work’s been done on looking at the genetics of brain tumours, but it’s generally been based on just one sample – one biopsy from within a tumour,” says Smith. “We’ve learnt a lot about brain tumours through doing that but, unfortunately, in recent years, we’ve come to realise that the answer you get depends on which bit of the tumour you take a biopsy from.”
To overcome this problem, Smith is studying the differences in the genetics and biology found between different parts of individual brain tumours: “By taking an overview of all the different bits of the tumour, we can hopefully describe the tumour’s genetics better and develop more effective targeted therapies against brain tumours.”
Accessing the brain
Smith’s also looking at ways to make sure anti-cancer drugs reach their target: any cancer cells, high or low grade, that cannot be removed by surgery. This can be especially challenging with brain tumours.
“There’s a barrier between the blood stream and the brain – the blood-brain barrier – that acts to protect the brain in normal life. Unfortunately, the body and the brain think that chemotherapy drugs are toxic, so the barrier also excludes these drugs from the brain.”
Chemotherapy drugs, which are often injected directly into the bloodstream can get through the blood-brain barrier, but the dose needed to do so would cause toxic side-effects for the patient.
To get over this hurdle, Smith is working on implantable pastes that can deliver chemotherapy directly into the brain: “If we can bypass the blood-brain barrier and get the drug more effectively to where it needs to be, we could achieve a higher concentration within the brain but a lower toxic dose to the patient.
“Ultimately, that would mean a more effective treatment with fewer side effects.”
Kerry Noble is a freelance science writer
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