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According to DSM-5, with OCD, the disturbance is not better explained by the symptoms of another mental disorder such as preoccupation with having an illness, as in illness anxiety disorder.
In his case, he was previously dx with cancer, treated, then develop these anxieties that he may have missed some sign is more fitted with illness anxiety disorder.
Moreover, OCD is characterized by ego-dystonic, which is "thoughts, impulses, and behaviors that are felt to be repugnant, distressing, unacceptable or inconsistent with one's self-concept", which clearly doesn't apply to the pt case, as checking the temperature is actually meaningful and goal-directed.