How can you feel alone when you're surrounded by people? Lisa Grice from Cheshire knows the answer to that because in 2012 when she was diagnosed with endometrial cancer, she had her husband by her side - but she was still crippled with loneliness.
And it was that loneliness, compounded by anxiety, which prevented the mum-of-three from attending the treatment appointments that could save her life.
Lisa, 55, needed a doctor to reassure her about treatment. She needed to speak to someone who had experienced cancer and could answer her questions, but the support wasn't available. So, feeling unable to cope, she buried her head in the sand and refused to have treatment, despite the desperate pleas of her family.
Sadly, Lisa's story is more common than you might think. Macmillan Cancer Support estimates that there are 21,000 lonely cancer patients in the UK each year who struggle to follow their treatment plan.
That's a huge number of people - enough to fill the O2 arena. Imagine all those people, already struggling to cope with the devastating news that they have cancer. Now imagine that they are going through it feeling completely alone. Heartbreaking, isn't it?
Loneliness has dominated the news agenda recently. We know that it can be as harmful as smoking, that the UK is the loneliness capital of Europe. We also know that, contrary to popular belief, loneliness doesn't just affect elderly people. Macmillan's research found that cancer patients under 55 were twice as likely to say they were lonely than those older than 55.
What is particularly worrying though is the impact that loneliness can have on cancer patients. Macmillan's research shows for the first time that the recovery of lonely cancer patients could be at risk as they are three times more likely to struggle to follow their treatment than patients who aren't lonely. In short, loneliness coupled with cancer can be toxic.
Not attending appointments or being unable to pick up prescriptions brings with it a plethora of problems. If you miss a chemotherapy treatment for example, your doctor will be unable to monitor the impact of the treatment. You'll be more susceptible to developing infections which could be life-threatening if they aren't treated immediately. If you're unable to pick up your prescriptions and medication, you may be in pain or distress, or experience crippling side-effects.
Of course, if you refuse cancer treatment altogether the situation can become graver still, with your chance of survival diminished. A Canadian study of breast cancer patients showed that those who had treatment were twice as likely to be alive five years after diagnosis, than those who refused.
That's a real concern for Macmillan, to think that there are people out there - someone's mum, brother, grandparent - who might not survive their cancer because they're lonely.
You might wonder how loneliness can prevent patients from following their treatment plan. Maybe they live far away from friends and family and don't have anyone to physically take them to their appointments or to the chemist to collect their prescriptions.
Maybe they are a carer and feel they can't have treatment because there will be no-one to look after their loved one while they are in hospital. Maybe they worry that having treatment will prevent them fulfilling their carer duties. Or maybe, like Lisa, they are so scared and anxious that without intervention from a medical professional they don't feel emotionally strong enough to attend appointments.
By 2020, almost one in two of us will get cancer during our lifetime. With loneliness putting people's recovery at risk, we need to tackle the issue now.
Thankfully, there are solutions. For Lisa, it was the support and advice she got from Macmillan Cancer Support's 24-hour online community. By talking to other cancer patients, Lisa found the strength and encouragement to attend her appointments and she is now in remission.
As well as the online community, Macmillan Cancer Support provides a telephone helpline (0808 808 00 00) which people can call if they need someone to talk to. We also have over 6,000 Macmillan professional, nurses and GPs, who can offer support.
Sometimes, what patients really need is peer support and that's why we have set up befriending or buddy schemes which are being piloted around the UK. We pair up newly diagnosed cancer patients with someone who has had a similar experience so they can meet in person or chat over the phone. This means the patient can speak to someone who truly understands what they've been through.
We want health professionals to identify lonely cancer patients by asking all cancer patients if they live with anyone or have friends or family who can support them during treatment and beyond. We want them to direct lonely cancer patients to alternative forms of support.
We all have a part to play though. If your neighbour, friend or relative is diagnosed or treated for cancer, make sure you're there for them. It's too easy to say: 'Let me know if you need help,' but often people feel too embarrassed to ask. So make a casserole, stop by for a chat, offer to drive them to appointments. Let's bring back compassion and kindness in our communities and make sure that no one goes through cancer alone.
Follow Juliet Bouverie on Twitter: www.twitter.com/JulietBou