A statement posted to her Instagram by her children said their "incredible mother" died on Monday afternoon at Martlets Hospice in Hove.
"In July, Mum was diagnosed with a stage 4 Glioblastoma, a fast-growing and highly aggressive malignant brain tumour," it read.
"In the four months that followed, she displayed remarkable resilience and strength, despite undergoing brain surgery and countless radiotherapies.
"In her final weeks, she was passionate about raising awareness for Glioblastoma, embodying her lifelong commitment to helping others."
Giles wasn't the only celebrity keen to raise awareness about brain tumours. Last year the late Tom Parker's widow Kelsey also called for more funding into brain tumour research in the UK, after The Wanted singer died at a hospice near the couple’s south-east London home at the age of 33, following his diagnosis with stage four glioblastoma. Early detection is key.
So, here's what you need to know about brain tumours, from symptoms to treatments.
What are brain tumours?
A brain tumour is a growth of cells in the brain that 'multiplies' in an abnormal, uncontrollable way, according to the NHS. There are different 'grades', including one and two that are low grade, and three and four that are high grade.
The two main types of brain tumours are non-cancerous (benign), which are low grade and grow slowly and are less likely to return after treatment.
Cancerous (malignant), meanwhile, are high grade and either start in the brain (primary tumours) or spread into the brain from elsewhere (secondary). These are more likely to grow back after treatment.
What are the symptoms of a brain tumour?
Symptoms of a brain tumour vary depending on the exact part of the brain affected.
They might include:
persistently feeling sick (nausea), being sick (vomiting) and drowsiness
mental or behavioural changes, such as memory problems or changes in personality
progressive weakness or paralysis on one side of the body
vision or speech problems
"Depending on which part of the brain the tumour is affecting, the symptoms can vary," Dr Daniel Cichi from Doctor 4 U emphasises. "If, for instance, a tumour is located at the frontal lobes this may cause personality and behavioural changes.
"Symptoms can vary greatly amongst patients, but in general, any noticeable changes to your behaviour, mobility, vision or speech should be checked out by your doctor."
Dr Cichi says that in particular, if you’re experiencing frequent and severe headaches, loss of sensation or movement in your limbs that happens gradually, or progressive weakness on one side of the body, as well as seizures or speech and vision problems, these could indicate a brain tumour. But, he cautions, it’s not always the case.
"Nausea, vomiting, drowsiness and headaches may be the more subtle signs of a brain tumour as many people put these symptoms down to tiredness, working too hard, or other illnesses," he adds.
"But anyone who is experiencing headaches, which are out of the ordinary for them should speak to their GP as soon as possible."
Watch: Woman loses all her childhood memories after life saving surgery to remove brain tumour
Brain tumour treatments
As mentioned above, not all brain tumours are cancerous and some are less complicated than others, depending on where the tumour is located, among other things.
"Non-cancerous tumours can often be removed successfully with surgery and they very rarely grow back," Dr Cichi explains.
"In some cases, a person may be able to live with their benign tumour for quite some time before they have surgery because they are slow-growing compared to cancerous tumours which grow at a much faster rate."
Cancerous brain tumours can also be treated with surgery, as well as radiotherapy and chemotherapy if not all of the tumour could be removed in surgery.
"Different types of speech and physical therapy may be given if the tumour has affected motor skills, vision, and speech," Dr Cichi adds.
Again, depending on the type, after initially being diagnosed with a brain tumour, steroids may be prescribed to help reduce swelling around the tumour.
Other medicines can be used to help with other symptoms of brain tumours, such as anti-epileptic medicines for seizures and painkillers for headaches.
What causes brain tumours?
Often, the cause of a brain tumour is unknown, but according to Dr Cichi they're more likely to develop in old age.
While most happen in 85 to 89-year-olds, they can affect people of any age, including children.
"Genetics (family history) can also play a part, and we know that exposure to radiation can increase the risk of developing some types of brain tumours," he adds.
While this only accounts for a small number of brain tumours, some types are more common in those who have had radiotherapy, CT scans, or X-rays of the head.
What is glioblastoma?
Glioblastoma multiforme (GBM), the type of brain tumour Giles had, is the most common type of brain tumour that starts in the brain.
According to The Brain Tumour Charity, it is the most aggressive form of adult brain tumour and is often resistant to treatment.
It is believed that the variety of cells in a glioblastoma is one of the reasons it is so hard to treat, because current drugs are not able to effectively target all the cell types in the tumour. As with most brain tumours, the cause of glioblastoma is not known.
Brain Tumour Research says the first option for the treatment of GBM, if the tumour is operable, is surgery, usually followed by radiotherapy and chemotherapy.
"The surgical operation to remove a GBM is a delicate balancing act between removing as much of the tumour as possible and protecting the function of the healthy brain," says a spokesperson for Brain Tumour Research.
"So the location of the brain tumour is very important with regard to both the potential impact of surgery and the symptoms that the patient will experience (because different areas of the brain control different mental and physical processes).
How much of a glioblastoma a neurosurgeon can remove is limited because GBMs are 'diffuse', meaning that tumour cells invade healthy areas of the brain adjacent to the tumour. Unfortunately, the nature of GBM means some tumour cells will almost always be left behind and hence will continue to grow.
For this reason, radiotherapy and chemotherapy are the next stages of treatment for a GBM. Usually, people are offered the chemotherapy drug Temozolomide (TMZ) alongside radiotherapy, and then further doses of Temozolomide afterwards.
For more information visit the NHS's website page on brain tumours.
You or your loved one being diagnosed with brain tumour can be frightening. But as well as your doctors and medical professionals being there to guide you through it, further support is out there too – visit The Brain Tumour Charity's website or call its helpline on 0808 800 0004.
Additional reporting PA.
Brain tumours read more:
Neurologist reveals the anti brain ageing routine you should do every day (Yahoo Life UK, 7-min read)
Woman’s ‘ear infection’ turned out to be a sign of a brain tumour (Yahoo Life UK, 4-min read)
Husband and wife both diagnosed with brain tumours 14 months apart (Yahoo Life UK, 4-min read)