Step 1: Recognise the drainage pattern. The tongue's lateral border drains readily into the cervical nodal basins, so tongue cancers are notorious for early, sometimes hidden, neck spread.
Step 2: Decide on the neck. Because of this nodal risk, treating the primary alone is inadequate. The standard is to clear the regional nodes via a modified radical or selective neck dissection.
Step 3: Rule out the alternatives. Plain observation gambles on missing microscopic nodal disease. Radiotherapy after surgery is reserved for adverse pathology like perineural invasion, lymphovascular invasion, or proven node positivity, and chemotherapy is not the first locoregional move.
\[\boxed{\text{Neck dissection}}\]