There are not enough NHS staff to meet the needs of growing numbers of people with cancer, a charity is warning.
Macmillan Cancer Support says patients are calling its helpline "at breaking point", feeling they cannot ask questions of the overstretched doctors and nurses caring for them.
Key targets for cancer care are being missed as pressure on the NHS rises.
The NHS said patient satisfaction levels and survival rates were both at record highs.
Health ministers in England said they would make sure the NHS had 50,000 more nurses by 2025.
The cancer charity's helpline received more than 240,000 calls this year, with most people needing emotional support, as a result of anxiety or fear over the disease.
This was followed by issues with accessing hospital or community care, including difficulties contacting medical staff or getting hold of specialist medical equipment for use at home.
Callers needing this kind of help have been rising for the past few years, outnumbering those calling about pain and side-effects of treatment, Macmillan says.
'Rushed off their feet'
Mandy Mahoney, 48, an outreach support worker from London, was initially diagnosed with breast cancer in 2011.
She said: "In recent times with the pressures on the NHS, I've become less likely to contact the hospital for fear of being a nuisance, but this has an impact on my mental health."
Ellen Lang, a service manager on Macmillan's Support Line, said: "When you only have 10 minutes with your doctor, and your nurse is visibly rushed off their feet, it's inevitable that you'll leave without all the answers you need."
Lynda Thomas, chief executive at Macmillan Cancer Support, said it was "heart-rending that so many people call at breaking point having struggled to find the support they need from their healthcare team.
"NHS staff do an extraordinary job faced with huge pressures, but as increased demand for our services shows, there simply aren't enough of them to meet the needs of the growing number of people living with cancer."
The NHS target is for 85% of patients given an urgent referral by their GP to start cancer treatment within 62 days.
However this target was last met in December 2015. Last month, NHS England figures showed that 76.9% of cancer patients started treatment within two months.
Cancer targets in Scotland and Wales are also being missed.
Rising numbers of people with cancer are being referred for treatment, NHS England said.
Cancer survival 'record high'
In a separate report by Macmillan, 44% of specialist cancer nurses said their workload was having a negative impact on the care they gave to patients.
And nearly one in five people recently diagnosed with or treated for cancer, said the doctors and nurses who cared for them seemed to have unmanageable workloads.
An NHS spokeswoman said: "Most importantly cancer survival is at a record high, and so too is patients' satisfaction with their care, with nine out of ten patients happy with the support they've received, all of which is testament to the hard work and compassion of NHS staff".
The NHS aims to give every person diagnosed with cancer "access to personalised care plans including a needs assessment and health and wellbeing support" by 2021, they added.
A Department of Health and Social Care spokesperson said there were plans to roll our "hundreds of new diagnostic machines across the country" and boost nurse numbers by 50,000.
"There are already tens of thousands more doctors and nurses on our wards since 2010 and we're investing an extra £33.9 billion a year in our NHS within the next five years," he added.