In order to diagnose whether cancer is present or not, the entire tonsil needs to be removed (tonsillectomy). Taking only a small superficial sample of the tonsil via incisional biopsy is NOT recommended as it may miss the cancer if it is occurring deep within the tonsil.
As such, tonsil removal is not just for recurrent infections, but also to evaluate for presence of cancer and should be undertaken in patients where one tonsil is significantly larger than the other. Indeed, ENT's are trained to consider unilateral tonsillar hypertrophy cancerous until proven otherwise and diagnostic tonsillectomy should be pursued.
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Palatine Tonsils Asymmetry: 10 Years Experience of the Otorhinolaryngology Service of the Clinical Hospital of the Federal University of Paraná. Int. Arch. Otorhinolaryngol. 2011;15(1):67-71