My son has high IgE levels in blood, could the body be reacting to cancer?

Probably not. High ige levels are usually related to allergic disorders and some lung disorders. Cancer is not a common cause of high ige levels.
Allergy, parasites. An elevated ige is more likely to be due to allergy or parasitic infestation rather than reaction to cancer. Why were ige levels done? You should take up the matter with the doctor at the next visit.