No matter how common cancer is, it can be difficult to know what to say and do to help a loved one after diagnosis.
To mark, World Cancer Day, we've decided to look you can best support a loved one who has cancer.
We think this should include care and support from friends and family.
So, how can you help someone when they receive a cancer diagnosis?
"There is probably no right or wrong answer to what you should say to someone with cancer and what you shouldn’t," Hallenga tells HuffPost UK Lifestyle.
"I even struggle with what to say to someone when I find out they’ve been diagnosed with cancer - and I’ve got it!"
Hallenga says when she was first diagnosed, she preferred friends and family to say something, rather than nothing at all.
"But I think it’s about acting as normal as possible and not overcompensating with your behaviour when a friend has cancer," she adds.
"You don’t necessarily have to do anything big, just being there speaks volumes."
Fatigue can be one of the first symptoms of cancer. Unfortunately, cancer treatment can make feelings of exhaustion worse.
Helping a loved-one with everyday tasks can therefore have a big impact on their overall wellbeing.
“Cook for them - and clean up," Hallenga says. "My sister did that a lot for me during chemo and it was certainly one of the things I appreciated most."
Finding out you have cancer would be difficult for anyone to come to terms with. Add in a packed schedule of hospital appointments plus new medical terminology to get your head around and the weeks following initial diagnosis can be overwhelming.
Macmillan cancer information nurse specialist Angela Vincent has worked with cancer patients for over 10 years. She says you can help a friend who's recently received a diagnosis by helping on practical level.
"One of the first things you can do is to help someone to get information. Go to reputable websites from registered charities and organisations," she says.
"You can also offer to go to appointments with your friend if you have that kind of relationship and think it's appropriate."
If you're going to an appointment with a friend, Vincent recommends you take notes on their behalf.
"Doctors don't mind note-taking at all," she says. "When you're in a stressful situation, you only hear half of what's being said and you don't even necessarily understand all that.
"Making notes for a friend means they'll be something you can then both come back to together later. It can help patients work out what questions they still have."
Offering to help with transport, shopping and childcare can also make a really big difference.
So what should you not do if you find out a friend has cancer?
Vincent says referring to a third party's experience of cancer - such as "my colleague who had cancer..." - can be unhelpful, even if it is meant with the best of intentions.
"It’s not about that other person, it’s about the particular loved one you’re with at the time," she says.
She also notes that reminding a loved one to "keep positive" regularly can sometimes have a counterintuitive effect.
"It’s very tempting to say to someone 'stay positive, keep strong' but for most, it’s not very realistic," she says.
“If you’ve been diagnosed with cancer and you’re facing six months of cancer treatment, you’re not going to be positive all the time.
"I’ve looked after people who have said they’ve felt under a lot of pressure to ‘stay positive’ because, for example, their daughter has asked them to. But it can be more helpful to know that it’s okay to be negative sometimes as well."
Above all, Vincent says it's important to remember that your friend is still the same person despite their diagnosis.
"Just because somebody has been diagnosed with cancer, that cancer doesn't have to define them," she says.
The idea that you should treat a person with cancer as you always have is supported by Beauty Despite Cancer.
Jennifer Young created the site following the popularity of her skincare range for women undergoing cancer treatment, Defiant Beauty.
She tells us: "Women do not stop being women when they are diagnosed with cancer and friends should not stop being friends - our relationship with friends changes as we go through different stages of life, the changes can be for a short while or longer term.
"Who hasn't endured endless tearful conversations about a totally unsuitable man that you know (or hope) will be out of both of your lives before too long? That need is brief, soon you are on to nutrition for toddlers and school league tables.
"I am not trying to compare the devastation of a cancer diagnosis and treatment with any other life event – my point is, as a friend you adapt to the needs of your friend, you always have done and you can do it now."
It's natural to want to drop everything to help a friend who has been diagnosed with cancer, but it's also important to look after yourself.
If you know someone who has been diagnosed with cancer, remember to talk to those around you and seek help and support for yourself, as well as for your friend.
Check out Macmillan Cancer Support's new website The Source for more information on how to support a loved one with cancer.