One in four cancer patients in Devon faces isolation, according to new data from Macmillan Cancer Support, who have launched a campaign to tackle the issue.
According to the charity, of the 6,650 new patients a year an estimated 1,600 lack support from family and friends during their treatment and recovery.
Of these, an estimated 400 each year receive no help whatsoever, facing the disease on their own.
The Facing the Fight Alone report found the detrimental effects of such isolation is far-reaching.
David Crosby, general manager of Macmillan Cancer Support in Central and South West England, said: "This research shows that isolation can have a truly shattering impact on people living with cancer.
"Patients are going hungry, missing medical appointments and even deciding to reject treatment altogether which could be putting their lives at risk all because of a lack of support.
"But these figures are just the tip of the iceberg. As the number of people living with cancer is set to double from two to four million by 2030, isolation will become an increasing problem."