Four days after a dentist flagged a swollen lymph node, Ethan Harrison, 19, was admitted to Chesterfield Royal Hospital and diagnosed with acute myeloid leukaemia.
Doctors told his family the timing was critical: had he not gone to hospital when he did, he may have had only three weeks left to live.
Harrison began chemotherapy last week and is expected to undergo four rounds, starting with a month in hospital receiving two medications twice a day.
His mother postponed a new job and Harrison took sick leave, with the family expecting roughly a year of recovery and long stretches in hospital.
Nearly £3,500 has been raised in a week through a GoFundMe launched by friends as the family adjusts to the sudden diagnosis.