In spite of his immense recuperative capacity, Fox found that by late August he was exhausted before he began his day's run. On September 1, outside Thunder Bay, he was forced to stop briefly after he suffered an intense coughing fit and experienced pains in his chest. Unsure what to do, he resumed running as the crowds along the highway shouted out their encouragement. A few miles later, short of breath and with continued chest pain, he asked Alward to drive him to a hospital. He feared immediately that he had run his last kilometre. The next day, Fox held a tearful press conference during which he announced that his cancer had returned and spread to his lungs. He was forced to end his run after 143 days and . Fox refused offers to complete the run in his stead, stating that he wanted to complete his marathon himself.