A gruelling course of chemotherapy caused his weight to plummet to just two stone.
So when five-year-old cancer patient Lewis Mighty put on a few pounds, his mother was overjoyed.
Until, that is, she received a letter from the NHS bluntly telling her that Lewis was overweight.
With astonishing insensitivity, it warned her that he was at risk of cancer - despite being just two pounds over his recommended weight.
The letter suggested Lewis should take up swimming, even though an intravenous drip in his chest to deliver life-saving drugs prevents him from being in water.
One-size-fits-all medicine, using a bullshit BMI-type scale I don't doubt.
She also said Lewis's consultant 'couldn't believe it' and speculated the NHS officials are not using an up-to-date system for calculating children's healthy weight.
The letter comes days after the parents of healthy five-year-olds Gracie Hill and Bailey Russell received similar warnings from NHS Derby City that they were overweight.
Like their parents, Lewis's mother said she had decided not to tell her son about what had happened as she thought it might upset him.
'If they pumped as much money into diagnosing cancer as they do into weighing and measuring the kids, we wouldn't be in this position,' she added.
Ah, but that wouldn't give them this kind of control of your lives...